My mechanic said my 97 Accord has a rear main seal oil leak, which he can't fix unless I want to pay him thousands to remove the transmission first. A few months ago I noticed the oil had stopped leaking. Maybe the oil had gotten dirty and thickened enough to stop leaking. Then I got an oil change (presumably with synthetic oil), and it started leaking again.

I want to top off the oil, but what would be best to use to stop the leaking? The 97 Accord normally takes 5W-30. Would a conventional oil be thicker than a synthetic oil? Or would it be better to try a 10W-30 oil?

 

I would stick with 5w-30, because that oil weight is what provides the best wear protection in your engine. Just have a quart of oil in the trunk to ensure you can top off the level.