Well, in the future I think I will remember to spray the cleaning solution (Amorall Cleaner in this case) on a towel to clean the printers and get the loose toner off.
Apparently after changing one of the toners in one of the HP 4550s today, I sprayed the cleaner on the printer and it got sucked in. This caused splotching on the color printouts going forward.
After swapping several parts with the "standby printer", I read the troubleshooting guide which suggested the transfer roller. When I got home tonight I swapped transfer rollers and that solved the problem / moved it to the other printer. Fortunately the transfer roller is about $27 from a number of sources and I found a new one on Ebay for $10 (shipping included). Actually the transfer roller probably was on its last legs anyway as I bought the printer used and it now has about 45000 pages on it. The transfer kit including the roller is supposed to be done every 25000 pages or so. Current Mood: tired