I recently bought a big Roto 4 stroke for my 1/3 scale cub, and its a work of art. After receiving the engine and getting a number of emails from roto about my concern of "what oil" must be used for this engine. My question is do I have to use motul 710? I have always used stihl ultra hp for everything, but from what I get from them is that they only guarantee the engine if you use "their recommended oil" I mean I can switch to motul but stihl ultra is right down the street from me. thanks for any input.