I've had the same experience - switch to synthetic, leaks start right away, change back to conventional oil and the leak stops. There are still people who swear that the tendancy for synthetic oil to leak is an old wives tale. The theory goes that it was a problem when synthetics first came out but then they put in stop leak additives and solved the problem. Seems to me you can just look at the stuff pouring out of the bottle and see that it would be more prone to leak. It pours just like water. It's got just to be more prone to leak than something that pours like molasses.