The early MDS had leaky carburetor o-rings but that got fixed after a few years. I initially had a .61 that had a lot of power but developed a leaky o-ring after 2 years. Believe or not they replace the engine free with a .68 which worked like a charm. The biggest issue I knew of with them was a bias against a (whether true or not I don't know) "Russian" engine. I think the .48 and .68 were later engines, the .40 could be either.