Synthetic oil does not create leaks, it finds them. Probably because it flows so much better.
When I got my car I replaced the 20W-50 dyno with 5W-30
synthetic, my
oil pressure went up! I figure it was because the
synthetic had a much easier time going through all the plumbing (including the cooler) on its way to the engine (and pressure sensor).
Many owners using heavy
oil may be getting more pressure at the expense of reduced flow.
My $0.02
Bob