I have a book for 1998 843- It gives the pump as 25-12057. Northern Lights number. Check with Depco in Lauderdale. Cover plate on pump usually gives mfr (Johnson???) and part number. NL does not make the pump, they buy it from I think Johnson. Edit: Jabsco, see below.
You may need a puller to get gear off the tapered shaft unless pump comes with one.