Does anyone know where I can find a wastegate servo/diaphragm for my '91 350SDL?

I noticed power under hard acceleration was reduced recently. Assuming there was no boost, I found that the wastegate was closed. Under further inspection, I found the wastegate servo would not actuate under vacuum.

The dealer says that the servo is part of the turbo assembly and can’t be purchased separately!

Any suggestions?

Mav

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'91 350SDL 165K miles
Lovin' her until she blows...
'01 Dodge Ram Cummins 4X4 DWR
Stump pullin' beast...