I just read in some other posts that switching a high milage car to synthetic oil from regular could cause leaks. Well, I bought my '94 850 wagon last year and I was sure it did not leak at the time. I have been using sythetic and over the past year it has been leaking worse and worse from all seals. Today it is in the shop getting new valve cover gasket and rear main seals. It never occurred to me that the oil could cause this, I just assumed it was time for them to give out. How is it possible for synthetic oil to do this - does it degrade the seals or something? Is it a chemical reaction with the rubber after being in contact with organic oil for years? And now that I have new seals should I go back to natural oil?

Confused oil changer :)