Turbo Quattro Coupe Wastegate II

[bruceh@garlic.com (Bruce Hochuli (Ventana Computer Corp.))]

PART 2 of wastegate saga

My mechanic has convinced me that my wastegate diaphram is cracked
and that the spring is weak. What I want to do is replace these
two (maybe one) simple parts. Where can I get them? With all of
the people making wastegates, surely some one has one the same
diameter. Getting the spring just right concerns me less since
I have adjustable boost. 

Has anyone else out there had this problem?? Is there a cross
over part from a Porsche or something else?

The car is a 1982 Turbo Quattro Coupe with about 150K miles.