am no expert but I have had 2 one of then had a jb pump head upgrade think it had 2 0 rings instead of one if I remember righty
easy enough to work on
seals on the pump head need changing very offend as they take some pounding and you need to use a very little oil on the seal think jb said to use some thing ??50 count remember the name but he'll soon tell you very help full bloke
you have to adjust the pump rod to get the max out of the single stroke but once set I could get 11.5 fpe no probs