On mine it was the rear tranny mount. Can be a bear to see the condition, as it wasn't until I removed it that I could see it was totally collapsed .

Good luck!

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‘84 300TD “Mountain Goat”
'62 300d Adenauer-350 Chevy - "Max"
'15 VW Passat TDI
'16 Dodge Ram 3500 - Cummins w/6-speed
'68 Mustang fastback
'55 T-bird
‘63 Studebaker Hawk