once you switch to synthetic, you really really should not go back, but if you do on accident, its recomended you never look at the syn ever again. your rings really do not like switching.

 

eh, I think that's a myth...

 

do I smell the next episode of Myth busters?

 

No. I farted. Sorry []

 

What's the difference?

Seriously ... switching back and forth between synth and old school shouldn't be a problem.

... I still think you should have run longer on dino oil after your rebuild. You'll know for sure how well the rings seated if you start sucking down the synthetic. I suppose you can always switch back for a while to continue the break-in if you have to.