synthetic oil leak
I can verify what a number of messages have said about older engines, changing to synthetic oil, and leaking. With 20-50 dino, I had an occasional drop of oil, maybe about 1 or 2 times a week. I changed to 5-30 about 2 weeks ago, and immediately began dripping a drop or 2 every night. (From either the rear seal, head or valve gasket; no one can seem to say for sure....)
My mechanic said it had been a mistake to change, and that with synthetic I could expect to develop leaks. He said the main problem was that once the oil began to leak through seals, it essentially, as I understood him to say, opened up the seals or holes in the seals, and switching back at that point would do no good. The damage would have already been done.
So, I switched back to 20-50 yesterday, and this morning found drops of oil!
I have a 73 450sl with 112,500 miles.
I think the lower viscosity may have had something to do with it, but my mechanic said that even higher viscosity synthetic was a bad idea. He said synthetics were really formulated for more modern engines, especially turbos.