I have also had great results with Valvoline's MaxLife oil & ATF Stop Leak. Note: I also had very minor tranny seal leaks.

I used MaxLife oil in my 91 300E to resolve valve seal issues/oil consumption. The MB was eating about 1 QT every 1K and has 130K miles on it. I had great results so far, 2500 miles and have not added any oil. If I planned on keeping the car for many years, I would fix it properly by doing a valve job.. I would assume the worst the seals are the less effective it would be.

I believe most additives are worth less, but in my case the Valvoline products mentioned above worked for me..