Hello and welcome! I have one of those Mark 10’s also. The water pump is a real problem for sure. Elmer K’s parts list are barely readable and in my opinion not much help. I would suggest checking the hardware stores and maybe harbor freight for an O ring. Hope you found an impeller. Someone on here will probably chime in for one of those. I found an impeller that I had to file the key way a little and if my memory serves me correctly I had to ream it out a little. These motors run good and remember to be gentle when you shift it.
dale
