I would replace any external o rings, and seals you can. Trans filter and fluid a given, including converter. It would be an easy job to do your flex discs, center support, and u joint now too. Check for seepage of the rear main seal on the engine. Easy time to fix it.

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1959 Gravely LI, 1963 Gravely L8, 1973 Gravely C12
1982 380SL
1978 450 SEL 6.9 euro restoration at 63% and climbing
1987 300 D
2005 CDI European Delivery
2006 CDI Handed down to daughter
2007 GL CDI. Wifes