Last summer, I posted a document about rebuilding the oil/water pump (available here) Since August, 2 people have posted videos on Youtube. They are for a K1100, but this is the same as the K100. With all this information, you should be able to rebuild yours if needed.

Bert

Lots of great info on water/oil pump rebuilds out there, here is a few things I found in doing my 1985 k100RT.
The weep hole on the bottom of engine was completely clogged which resulted in oil in the radiator overfill tank, a pain to clean out. Turns out the hole does not go strait up but angles backward. The pumps actually stopped leaking after I cleaned out the holes and sprayed oil up in there but decided to rebuild anyway since I already had bought parts.
Took me awhile to find all 7 bolts holding pump on, cemented under 25 years of gunk.
My bike had the old style shaft with nut and cast impeller. The new shaft 11411461183 had the wrong gear, had to press it off and replace it with the one from the old shaft.
Some care full measurements showed the new seal 11411469329 to be a little too long, dealer recommend I buy a new stamped impeller and hub, I reused the cast impeller by machining 0.075" from the face that contacts the seal. An easy job on a lathe or milling machine, could probably get by with a grinder. Got about 1000 miles with no leaks.
Other parts, 11111460392, outlet O-ring, 11511704084 coolant seal, 012311460853 impeller bolt, 011411460328 shaft O-ring
When tapping the seal into the housing I had some small pieces of ceramic crack off, next time I will use a press and slightly larger socket or less hammering.
Cheers