I used (?) Prestone (?) with leak prevention. It doesn't temporarily swell the rubber seals, it rejuvenates them. I've used it for the first time when I bought this car some 8 years ago. It stopped the leak nearly immediately, and has been working ever since.

I read bad stuff about the other type, which temporarily swell your seals to stop leaks, I heard that one day it stops working and you lose all your fluid in very short order.

1991 300d, 191k