I also use Synthetic oil (Mobil 1) in my rotary for over 5 years with no problems. I don't have the stock oil injection system working as I prefer to premix 2cycle oil instead. Alot of the horror stories accour because synthetic oil dosen't burn, therefore if it's injected into the rotor it can gum things up. Im not an oil specilast but I know one, and he told me that synthetic oil that is 5000 miles old is better than new dino oil. With switching to synthetic oil and no other changes my oil temp went down 10 deg and my water temp decreased 15 degrees.