If I read your post correctly, you are saying the motor, if left to its druthers, parks with the bolt exposed when the wipers stand high on the window. That pins the problem on the cam and contacts in the gearbox. That is, if you're sure that bolt is tight and its motor shaft's keyway locked into the slot of the driving arm.

Aside from that keyway issue, I have no experience with what could force that cam to be out of "clock" with the drive. Most folks would just swap in a new wiper motor, or did you say that was already done? If done, double check the keyway.


--
Art Benstein near Baltimore

I can't believe no-one submitted this classic engineers joke yet:

A man is flying in a hot air balloon and realizes he is lost. He reduces height and spots a man down below. He lowers the balloon further and shouts: "Excuse me, can you help me? I promised my friend I would meet him half an hour ago, but I don't know where I am."

The man below says: "Yes. You are in a hot air balloon, hovering approximately 30 feet above this field."

"You must be an engineer," says the balloonist.

"I am," replies the man. "How did you know?"

"Well," says the balloonist, "everything you have told me is technically correct, but I have no idea what to make of your information.

"The man below says, "You must be a planner."

"I am," replies the balloonist, "but how did you know?"

"Well," says the man, "you don't know where you are, or where you are going, and you have made a promise which you have no idea how to keep. The fact is you are in the exact same position you were in before we met, but now it is somehow my fault."