The authorized repair folks have been hard to find but I finally got a
good response and things are on the way. I found the Service Bulliten
#632 on the Kohler website.

BTW. I dug enough chunks and bits from an old impeller out of my heat
exchanger to make a new impeller out of and she now runs great. It was
really easy to extract the exchanger and I din't have to replace any
seals.