in case this helps someone.. I think I have figured out the part numbers for newer and older pumps (disco 1 v8)

 PRC9409 (older type)
Takes wiring harness with round plug. (maybe STC3683)

ESR3926(newer type - faster transfer rate?)
Takes wiring harness with square plug. (maybe YMT100050)

the change to newer pump was around 1994.