I wonder what influence good maintenance/oil type has on the trransmissions? Both my cars, the 84 300TD and the 85 300 SD Turbodiesel have just under 300K miles. both have the original transmissions. I change oil about every 30 K miles. Never used synthetic oil.

Would it be recommended to continue as before or change to synthetic oil now? Are the seals, hoses etc. compatible for synthetic oil?

If you recommend a change to synthetic, what type would tyou recommend?

What are the high milage/no problem transmissions on the forum?

Lots of questions in hope to get more miles out of my trannies.

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1985 300SD Turbodiesel - wife's car
1985 300TD - my car