How long ago did you try it? I know syn oils USED to have problems w/ that (amsoil in particular when it first came out) but they all have the correct additives in them now. I STARTED using Mobil 1 in my 00 Cherokee @ 85,000 miles (when I bought it) and have had no problems. Same thing for my 01 Dakota...started using @ 60,000...no leaks. 65 Coronet...started @ 80,000 miles...no leaks. Bill M 65 Coronet 500 'vert On Jan 12, 2008 2:15 AM, Tom Watters <tomwatters@xxxxxxxxxxx> wrote: > > I tried using synthetic in an engine that had about 70K miles on it. > Started seeping at all the seems and had never leaked prior to that, > even out the valve covers. >