Mine has been leaking since 2007. Back then some were recommending Lucas Transmission Fix which is about $13 a quart out here. The claim is it stops leaks, hard shifts, controls overheating and renews worn fluid (I am reading this off of a sticker on the bottle). There is more on the actual bottle.

It never stopped the leak on mine but it significantly reduced it did help with some shift issues also but nothing spectacular.

Subjectively it reminds me of STP but pink. Perhaps all it really does is make the Transmission fluid thicker which of course would make it leak less.

Since I can do that myself at some point I should pull the transmission and replace the seals.
However, I replaced as seal on a chevy gasser and that worked for about 6 months and it started leaking again. I was looking for a reason why the new seal was not working and I pulled the transmission I also pulled off the front pump and I found that the front bushing was loose. So the reason the seal was leaking was likely the bushing not supporting the shaft and too much pressure was getting to it.

The more I took apart on it the more I found worn out. I ended up rebuilding it myself but there is a lot of information on the transmission used in a chevy astro van compared to the ZF transmission.

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84 300D, 82 Volvo 244Gl Diesel