95 Sea Doo HX problems

I recently purchased a 95 HX with a rebuilt engine.

It has some problems: Although the engine runs strong the it appears
that the driveshaft seal is shot. Water is pouring into the hull, and
the driveshaft bearing appears to be shot as well. It looks like a
relatively easy job to pull the drive unit out and replace the seals
and the bearing. Am I correct on this assumption, or is this a
dealer job.

Second, the charging system appears to have failed or was never
working when I recieved the boat. Could the charging system have
failed because of the water in the hull? Is this a difficult thing to
fix?

Thrid, is it necessary to backflush the engine to rid the cooling
passages of debris like sand and stones. If so, how often?

Thanks for your help. Please respond off the list.