Wipers stop half way down windshield

[123 300D driver]

Hello, I have a curious problem with my W123. The windshield wipers work normally, exept for when I turn them off. When they are turned off, they stop half way between the top of the windshield and the dash. When I switch the wipers back on, they resume working normally from top to bottom with the full range of motion. Then swithing them off, same thing, they stop half way down the windshield.

It seems to me that there must be an electrical contact plate or something that is inside the wiper motor housing that determines the stop position. Could it have moved or worn?

Anyone ever have this kind of problem?

Gary