if you feel like spending $600 or so, get the unwired digital replacement for the servo and amp. a few members here have had good results and considering the price for a rebuilt servo, might as well go modern.

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1982 300TD 210K miles ("The Replacement" aka "The Anvil") - SOLD
1979 300SD 245K miles (never ending project)
2007 Pinarello F3:13
1995 Ducati 916 (SOLD, sniff)
1999 Ducati 900SSie (SOLD)