I fixed mine today. I think. The end of the stalk comes off very easily with a flat blade screw driver. there is a spring in there that can fly out (will fly out) keep the door and window closed!
slide the sleeve down carefully taking care of the way it all lines up.
clean the contacts and check the spring and plunger are free I didnt find anything wrong but having taken it apart and put back together again the phantom wiper action has stopped.

Bingo, this should be the first step. Use a good electrical contact cleaner (DeOxIt or whatever Radio Shack sells) and clean up the internals. I fixed a 123 combo switch this way and saved $70 on a new part.

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Respectfully,
/s/
M. Dillon
'87 124.193 (300TD) "White Whale", ~392k miles, 3.5l IP fitted
'95 124.131 (E300) "Sapphire", 380k miles
'73 Balboa 20 "Sanctification"
Charleston SC