In an article on synthetic oil today on the web in AOL the following
appears :

"At one time, those who switched from conventional to synthetics had to
stick with synthetics-there was no going back. Synthetics expanded
the seals in the engine; then, when conventional motor oil was used,
that engine sprang multiple leaks.

Usage
Now, while the companies don't recommend mixing or switching back and
forth, one company's synthetics are fully compatible with others and
compatible with conventional oils. The source of compatibility problems
was high levels of ester in the earlier synthetics. Considering the
consequences, it's best to verify this compatibility, either on the
company's website or with your trusted mechanic."

So when I said that switching to synthetic made my S420 engine leak, I
was right!! And then Old Heavy Carl, the local Stealership here in
Greenville, ran out of Mobile 1 and put dino oil back in and I found
out only by accident! So I never switched back and was mad ever since -
about 6 years!!!!! And no one in here would believe me - kept saying
the synthetic oils didn't make the engine leak. WELL THEY USED TO
------ SO THERE !!!!!!  HAHAHAHAHA !!!!!!

Of course the dratted engine ran fine till I dumped it this last week
and it had 147,800 miles on it. Sounded real good, actualy. Of course
the water lines would blow out, etc.

mcbrue finalyprovenrightly under the bridge in the trailer down by the
river

06 Rexus LS 430