no the oil filter is on the front. the cylinder sounds like it could be the block breather? Or perhaps the oil catch cylinder that is sometimes fitted inline with the block breather pipe. follow the pipes from it, if it pops into the bottom of the airbox then yeah its the breather/catch tank. shouldnt need to touch it unless its blocked, if it was you would see excessive crankcase prtessures and blowing oil out of all the seals. also if you take top hapf of airbox off and run the engine, you should see/feel crank case fumes come out of the pipe.