Thanks to everyone for suggestions on repair or replacement of my 914 turbo servo with the broken wiper. I learned more than I ever wanted to know about this sys ...
I think everyone on this list would benefit from knowing about an equivalent motorcycle servo for a lot less cash! I looked myself for such a part... no joy!
The picture shows the inside of my TCU wastegate servo where the tip of one wiper has broken off and is now stuck against (perhaps with dielectric grease) what appears to be a screen printed resistor ...