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?