Welcome , and nice story about your cars.

The golf 3 is not a wanted car over here. They are also very cheap.
Main reason is rust. You almost cannot find one without it
I think you should replace the tranny for another one . By far the best option and an easy yob.
They are also very cheap , I think a hundred bucks max. (over here )
I did read on your other topic You tried the oil mix trick already .
Maybee You can add some teflon addition too.
Sometimes this helps also a little.

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Rallyegolf 2.5 TFSI S-tronic Quattro
Rallyegolf