Wipers only work on high speed.
 

Once in a while they will move a little bit, stuttering, then stop moving altogether when on "normal" and intermittent speeds. Is this a common issue? Does anyone know what the fix might be (other then tearing apart the motor and transmission and rebuilding it).

I believe that's what I ended up doing some years ago on my 924S because, although they did work on normal speed setting, a place where I took it to get inspected said the number of wipes-per-minute was too low.

switch might be dirty or failed. what happens if you move the intermittent knob? get better/worse/no change?

Put the wipers on normal speed and check for power at the motor. If you have power, then the switch is working and it's probably related to the motor. What I found on mine was the motor wasn't getting a good ground and it didn't run on normal and ran slow on high speed. Putting a volt meter at the motor connector will tell the real story.

It definitely sounds like the way to go, but do you need to remove that damn plastic cover that looks like the wipers have to be removed for the cover to come off, to get at the motor connector?

You may have to the plastic cover, I don't remember for sure but after that you can unplug the wires and test for voltage. I had a thread on that somewhere..I'll see if I can find it.

The same thing happened to my '87 944s. I had to remove the motor from the car, take apart the motor and clean the contacts. Water must have gotten in there at some point and caused some rust. As far as taking the motor out I had to take the wiper blades off first, then take the black cover off. After that I had to take the blower out as well, just make sure that you are marking everything as you go or the wiper blades my not align correctly. It took me about an hour to do the whole thing but I own a shop so it's a little different for me. I took the motor out with the metal bracket attached and marked it in relation to where the motor cog is at so i would not mess anything up. When you are looking at the motor you just take off the three screws and pull the motor apart. Clean the contacts with 1000 grit sand paper as well as the shaft.