15-50 Mobil 1 Synthetic - I've used this in 4 rotaries.

 

I been using 10-30 castrol gtx for 3 years.. had no problems with it... but should i change it to synthetic.
and seems like castrol might not be best for rotary.. what other brand of oil is good for 3rd gen?

thanks alot.

 

Used 20w50 for the past two years in all the seasons, even winter...