I ride my friends 636 alot, it had the notorious shift fork issue which was not cheap to get fixed. Other than that he has had the front master cylinder go bad and it is now leaking oil but I think something just rattled loose at a track day and neither of us has cared to look at it yet. It has 15k on it and is in really good shape. Its fast in a straight line, but to me it doesnt handle as well as my CBR. Also seemed to get alot of vibrations through the grips.