Just got a t2 that is running synthetic and wanted know if i can switch back to the 20-50 I was running in my NA the reason is I have not got a clue as to what brand of synthetic he was using.

 

should be fine to switch back. The old leakage worries from switching happend back in the early 80's with the early synths. That has not been a problem in 20 years.

 

I thought synithetic was harder on the seals and didnt burn liknon

 

nope, generally the other way around for good quality synths.

All automotive motor oils, synth or conventional burn at or under 500F (most around 400F). Either way; radically lower than the combustion temp of a rotary engine.