the rear main job isn't that bad. If you have done a clutch before all you have left is dropping the flywheel. No biggie. and you are already in there so do a clutch job.

But to answer your question. Synthetic will make everything leak unless the gaskets are good. Synthetic is better for a turbo because of its good heat characteristics. With that said, if you don't take your car to the drag strip, or auto-cross it regularly, don't worry about it.

But if you really want to run M1 then don't do a straight switch. Much like changing food for a dog. Don't do it all at once; slowly add to each meal (oil change) until he is used to it. (5 or 6 meals er oil changes)

Hope that helps!

Andrew

I did a sudden dino to syn in my Audi a few years ago and clogged lifters, blew out the gaskets in the oil pans, made the rear main leak... so been there done that, got the merit badge! (it wasn't a fun one!)