I have the Hydropower off of the engine to replace the oring on the shift spool. I noticed that previous owner had installed a new clutch. Then I could see that the very end of the input shaft had been forced against the pto drive hub. There is a slight amount of wear in the crank thrust bearing, but not enough to cause this much contact. It looks like the pto drive hub has been replaced also. Looked up the part number and 101803AS was used on 1600 and early 1650. But later 1650 used part number 163904AS. Could I have the wrong drive hub? Anyone know the differences in these two parts? Thanks