I have a GD31 long tail,after initial break in I have been using Mobil 1 10/30 after 12 years I am thinking of changing to Rotella T5 semi synthetic 10/30 . Number one I can get the Rotella at a much cheaper bulk price.So any input would be greatly appreciated.

I would stick with what u have been running. At 12 yrs... i would wait till the next engine to change flavors. Just my 2c

Thanks for the great information. Just needed a little push!