Kitchen Aid is 100% correct. The cause of the problem is age and lack of regular use, the oils in the gearbox grease separate from the solids over time and the oil then leaks out at the planetary and sometimes where the 2 case halves join under the silver trim band.
If you are up for a small job knock the chrome trim ring around the planetary off and clean it out and wipe around the area it covers. It is called a drip ring for good reason, you may find it full of oil.
The grease Kitchen Aid used in their mixers is Food Grade and it's harmless.
You will find that the fuse gear has failed, it's either been overloaded or it's just worn out from use or maybe the lubricating grease has gone old and needs changing. That will be change the failed gear and replace the grease.
More likely the pedestal base is bent. Your local service agent has probably seen it before and should be able to bend it back flat again. It's a brutal process with a heavy soft hammer that you probably won't want to see.
There are several things that regulate the speed, we will assume that the adjustment has not been messed about with. If the governor on the motor armature that presses against the underside of the square black speed control plate at the back has not flown apart then I would replace the small pcb (phase board) on the top under the back cover. One screw and 4 wires hold it on.
The head bounce sounds as if the locking hook is not engaged properly when you slide the head-lock lever to the locked position.
If this is the case, you will need to disassemble the mixer to make sure the link from the lever to hook is not bent. Another possibility is that the slot in the base the hook engages. If this is broken away, the hook will not be able to hold the head in place (I sure hope that this is not the problem).
Just recheck that you really have put the brushes back in the right way, use a torch and look in the hole. The brushes can each go in 4 ways, only one of which will work. Look for the blocker and line it up with the cut off corner on the brush. It's normally at the back, one side at the top the other at the bottom. After that you need to be looking at everything you have done for a booboo. I doubt it will be water ingress. Make sure the switch contacts come together when the lever moves to position 1.
You really need to get a Multi meter and follow the power, you have replaced the phase board so we can probably discount it being that.
First check that the switch contacts behind the black control board are really touching when you move the speed control lever to turn the mixer on.
Next the cable, do you have continuity from the wall plug to the control board on phase & neutral, (Check green earth wire as well for the sake of safety) that will be the black wire and the white wire on the 2 lower plug in contacts on the black control board at the back.
Next remove the carbon brushes, do they have reasonable length and most importantly are they fitted correctly with the corner key aligned with the blocker at the bottom of the brush holder.
Next with brushes out check for field winding continuity. On the other side of that black control board to where the power comes in there will be a red wire and a white wire that disappear into the motor housing. One of the wires will have a circuit to one of the brass brush holders and the other wire will have a circuit to the other brush holder. The resistance of both of those circuits should be pretty much identical.
After you have done those tests you should begin to have a clue as to where the problem lies.
Something must be broken if the motor is turning and the planetary is not. It will be one of the following, we will start from the first point of contact with the armature
1) Worm gear broken (fuse gear) you say no teeth broken
2) Worm gear not broken but whole unbroken plastic part not gripping aluminium boss
3) Pin through worm gear broken or missing
4) Pin through centre (or bevel) gear broken or missing
5) Pin through small gear in planetary broken or missing
6) Pin through planetary hub centre shaft broken or missing
The most common ones in order of likelihood are, 1, 2, 3 and 6
www.ereplacementparts.com. I did a complete tear down and parts repair on my wife's Kitchenaid mixer. This is the site I used to get the needed parts. They were very helpful, fast and the parts worked great.
If it looks like the photo beside the blue panel above I'd say it's a KSM 90 so you should be able to find your motor brushes and a downloadable manual with the help of Google. If you are in NZ I have brushes and can copy the manual for you.
Next, the parts list will tell you what the part number is for the brushes and all the parts that make up the brush assembly. If you need to replace any part other than the brushes you will need to do a full tear down to do that. Also; remember that there are four different ways to replace the brushes but only one way will work. You need to be very careful to remember which way the old brushes come out, there is a beveled edge on one side of the brushes and the new brushes need to go back the exact same way or they will not reach the commutator on the armature and the mixer will not work until the brushes make that contact with the armature.
Lastly the reason that your mixer gets out of time is that over time, 8-10 years of use, the nuts on the speed control switch that hold the three timing screws in place simply get loose due to vibration and the screws can rotate in or out. Some times the screws vibrate loose and the mixer just will not turn on next time the mixer is used. Peeps then think it's broke and will not work so they sell it for parts and by a new mixer. When the only thing they need to fix it is a Phillips screwdriver , a small 3/8th open box wrench and about 20 minutes time to fix it.
Anyway I hope that this helped to answer your question. Please let us know if it helped and if not let me know and I'll try to help fixya.
Among the causes for the mixer not turning on are (in no particular order) --
The leaf-spring switch on the Control Plate is not making contact.
The Phase Board is defective.
Brushes need replacement.
Brush chamfered side not correctly oriented.
Bad armature or field coil.
Seized motor bearing.
Detached or broken Control Board spring.
Speed Control Link plastic end broken.
I am sorry to hear you are having problems with your mixer. To stop the oil leaking from the front of the mixer, you just need to remove the drip ring and give it a good clean underneath and this should stop the oil from leaking out. Below I have added a link and if you watch on the timing "1.28" you will see how to remove the drip ring.