Stir speed doesn't work - KitchenAid K45SS Classic Stand Mixer

Maybe replacement of the speed control will solve both the original and new problems

Ideally you need to fix what's bent and that normally would involve splitting the cases to get at and repair or change the speed control lever. If you don't want to do that then removing the back cover and altering the adjustments and maybe bending the switch contacts may make it operate at both ends of the speed control.

First congrats on the great mixer that you have. next the pro 6 or professional 600 series mixers are of an entirely different design than the one that you have even though they are both bowl lift. Do you really need 6 quarts capacity? The pro series is a 575 watt mixer BTW, and it will have more power available to you IF you are doing bread or a lot of food grinding, if that is a requirement that you have then the 6 / 600 series is the better suited mixer but if all you are doing is general medium to light mixing duties then fix and keep the K5SS it a great machine,

On models with the "STIR" speed, the RPM (Rounds Per Minute) is 60.
Set your mixer speed to "1" or "2" and do the following:
Put your hand near the Agitator shaft and allow it to brush your finger slightly. Use your
watch or clock and start counting the number of times the shaft touches your finger in
60 seconds. In your case, the correct STIR speed is 60.

When you said "the speed switch doesn't want to stay in the off position", you meant to
say "the speed switch in the OFF position does not turn OFF the mixer", or "the speed
switch physically cannot be moved to the OFF position"?

In any case, try to adjust the mixer speeds.
Obtain a copy of the K45SS Repair Part List from Kitchenaid.com.
Remove the screw holding the End Cover and locate the three screws from the Control Plate.
All three (2 top left and right, and 1 bottom) must be adjusted.

1. Loosen the lock nuts enough & Turn the 2 top screws clockwise until they cannot be turned
anymore. Leave the bottom screw alone for now.
2. Use a dab of white paint or paper whiteout to mark the positions of the Phillips screws.
3. Plug in your mixer and Set the speed selector to "Stir".
4. Turn each top screw One full turn couterclockwise (alternating between Left and Right)
Keep making one full turn at the time (for both left and right) until the motor starts running.
5. Put your hand near the Agitator shaft and allow it to brush your finger slightly. Use your
watch or clock and start counting the number of times the shaft touches your finger in
60 seconds. The correct count should be 60 RPM (Rounds Per Minute). If it is less
or more than 60, give each screw 1/4 turn counterclockwise or clockwise and start counting
again. Now tighten both lock nuts.
6. Set the speed selector to "6" and turn the bottom screw either clockwise or counterclockwise
to achieve a speed of 180 RPM.

For your reference, the planetary RPM's for the 5-qt. tilt-head Artisan Stand Mixer are as follows:
Stir speed - 60
Speed 2 - 95
Speed 4 - 135
Speed 6 - 180
Speed 8 - 225
Speed 10 - 280

You are not adjusting the screws correctly. All three screws (2 top left and right, and 1 bottom)
must all be adjusted. Here is how:

1. Loosen the lock nuts enough & Turn the 2 top screws clockwise until they cannot be turned
anymore. Leave the bottom screw alone for now.
2. Use a dab of white paint or paper whiteout to mark the positions of the Phillips screws.
3. Plug in your mixer and Set the speed selector to "Stir".
4. Turn each top screw One full turn couterclockwise (alternating between Left and Right)
Keep making one full turn at the time (for both left and right) until the motor starts running.
5. Put your hand near the Agitator shaft and allow it to brush your finger slightly. Use your
watch or clock and start counting the number of times the shaft touches your finger in
60 seconds. The correct count should be 60 RPM (Rounds Per Minute). If it is less
or more than 60, give each screw 1/4 turn counterclockwise or clockwise and start counting
again. Now tighten both lock nuts.
6. Set the speed selector to "6" and turn the bottom screw either clockwise or counterclockwise
to achieve a speed of 180 RPM.

For your reference, the planetary RPM's for the 5-qt. tilt-head Artisan Stand Mixer are as follows:

Stir speed - 60
Speed 2 - 95
Speed 4 - 135
Speed 6 - 180
Speed 8 - 225
Speed 10 - 280

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.

I don't know if it will work for you but move the speed lever from front to back a few times as fast as you can. This will polish the contacts. This is like the old fashioned TV tuners. People used to turn them slowly and then complain when they needed serviced every 6 months. Spinning the tuner knob kept the tuners working flawlessly for years.

replace the stir speed switch

check to see if magnet on bowl guard is still in place, it is on the right side.