Oil leak and synthetic oil

[ChameleonGreen]

My car has about 117k miles on it. It's a 97 V6. Around 104k I switched from Castrol 10w30 to that Castrol high mileage oil and ran that for two changes. Around 110k I switched to Mobil 1 Synthetic and i'm about to start my 3rd cycle on synthetic. Since I switched to synthetic the car has developed an oil leak that's dripping onto the exhaust pipe that runs by the oil drain plug. The mechanic I use, who works at GM but does all my work after hours for cheap, said it was the oil pan gasket. I asked him if it could be the rear main seal, and he said he's never seen a rear main go bad. That kind of set me back for a second because I thought that was very common, and if it was, he should know. He is obviously wrong if so many people have had theirs go bad.

Anyway, so I have an oil leak either from the oil pan gasket or the rear main seal. It's not that bad of a leak, but it got noticeable by smell after I switched to synthetic for a while. Before I would just see a very small amount of oil on the oil pan during oil changes.

So the question is should I just keep running synthetic until I can get it fixed, go back to regular Castrol that I used for like 40-50k miles, or maybe use that half regular half synthetic oil i've seen on the shelves. Of course i'll get it fixed eventually, but what would be my best bet to keep the leak small until then.

Also, assuming I could find the souce of the leaking during the next change, would that JB Weld product i've read about a couple time on here be of any use?

Thank you
George

[bobrules]

High Temp Black Silicone RTV is your friend in all oil leak related situations.

From what I've been told, once you go synthetic you can't go back. I believe the synthetic swells the seals/gaskets(to prevent leaks) and if you stop using it your going to have problems.

Rear main seal leak is pretty common, not sure how common on a V6, but an engine can get a rear main leak at 50k miles. Best way to track oil leaks is powerwash the engine bay/underside and put it on a lift and run the car and see where it comes from.

[JoshMcMadMac]

Synthetic "causes" leaks. You run conventional oil and it builds up deposits and "seals" itself around gaskets. You switch to synthetic too late in the game and you clean all those "seals" out and cause leaks. Going back to conventional oil should, eventually, reseal those locations that are leaking. But, if it is the pan gasket, I would go ahead and get it replaced and keep running the synthetic.

[SOONverySOON]

yes, I have also been told synthetic oil makes leaks worse. thats why I dont go to it. good luck.

[Dekay]

Yea, the reason you have the oil leak is from switching to Synthetic oil and the gaskets that were once sealed from the regular oil are now cleaned off.

You can't go back to regular oil after using synthetic, it's a very very bad thing to do.

Best thing you can do for the car is find the oil leak and have it fixed, wherever it's coming from.
And for the record, my car had a leak in the rear main seal at like 20k miles. It was fixed under warranty at the time.