Hi Graham.
Sorry for delay in getting back to you. I replaced my generator after 19yrs of service, mainly due to same problem as you have experienced. Finding parts! The fuel shut off solenoid was the last straw, as the genny needed to be removed from the boat to get to it properly & I was quoted £1,000 to remove & re-install from a local boat yard. I decided that if I was going to spend that sort of cash, I may just as well replace the unit with a new one & take advantage of the warranty that would come with it. I now have a new unit, a Pageuro 5000 (5 Kva & 4.5 Kw) which is an Italian unit, still powered by the same Farymann diesel engine.
The old unit, (badged as a Lister Petter but has a Farymann engine & a Zeuise alternator) has now been fully overhauled by myself, at much expense, new lift pump, injector pump, injector, fuel filter & pipework & of course a new fuel shut off solenoid. I also had the head & cylinder barrel off & was surprised to see that the cylinder walls, still have the "cross hatching" machining marks evident. This after 19yrs hard labour !!!
This unit will be available on E-bay, when I get around to it, @ a starting price of £1,500 due to the amount I've spent on it & the fact that the new one stands me in £6,500. They really are lovely little units which I couldn't be without.