I'm replacing the impeller and associated guts of the water pump on a 1999 Yamaha 90 HP 2-stroke. After removing the parts of the pump, down to the pump base/housing, I noticed that the pump base/housing has corroded and now has a small hole (1/8" dia.) in the bottom of one of the channels, near the drive shaft and appears to be exposing a rubber seal. Is it possible that I can remove the pump base/housing and replace it, without messing with the gear case? My manual suggests partially disassembling the gear case before prying off the pump base/housing; however I don't want to get into the gear case due to lack of knowledge/tools.
If the answer is that I will not likely damage any parts by removing & replacing the pump base/housing without disassembling the gear case, what other parts should I replace along with the pump base/housing to be sure that I have a clean repair job?