I disassembled mine (OS120FS), cleaned it, and reassembled it and it works fine. I am not recommending taking a working pump apart. It is clear that the pump in question is shot, so nothing lost by takingit apart and finding out what is wrong. Maybe something can be learned, heaven forbid. I would sure as heck take it apart and have a look before I put out the bucks for a Perry pump or give the engine up as a lost cause.

Regards,
doubledee