I rebuilt my oem starter in 2017. I bought a rebuild kit from ebay that I think was from China. I think I only used the new brushes and a couple of the o-rings/washers that seal the starter. I think I cleaned up the original brush plate and used it. The brushes had worn down and the commutator was dirty and cleaned up per shop manual. Cleaned and re-greased the bendix, bearing was good so did not replace. It has been fine ever since.
Also, do not jump start a Seadoo, you could fry the MPEM. Recharge the battery after disconnecting from the ski.