I had just the opposite experience, in two engines I've used synthetic oil in
which had minor leaks, the leaks stopped. Presumably from seals swelling a bit.

On Thu, Aug 08, 2002 at 12:50:48PM -0400, Kim Brennan wrote:
> In a message dated 8/8/02 12:44:41 PM, warmerwagen@HOTMAIL.COM writes:
>
> >I quit using synthetic after it turned my  Jetta  engine into a
> "Lubri-leaker".
> >Since I went back to dino the leaking has stopped. Maybe the brand? I used
> >Amsoil.
>
> Synthetics have the capability of better cleaning (suspending contaminants in
> the oil so that the filter will remove them.) This means that crud that you
> have in your engine that MIGHT be blocking leaks, may get cleaned out when
> you switch to a synthetic oil...and hence reveal the leak.
>
> It is usually the reason that switching to synthetics on USED engines isn't
> encouraged, but if the engine is new or rebuilt, it is encouraged.

--
Harmon Seaver
CyberShamanix
http://www.cybershamanix.com