I'm trying to repair my 450F where the crankshaft nut backed off into the inside of the case. I always thought that the 2003 2004 and 2005 shared common engine parts. Today I discovered today that even though the side cover gaskets are the same for 2003 thru 2005 the cover for the 2003 is a different part number than the 2004 and 2005(the part that houses the water pump, oil filter and kick starter shaft seal). Does anyone know what the difference between 03 and 04? Can a 2004 or 2005 work on a 2003?