Update time.....
Friday night, half an hour spent taking off wheel, separating balljoint, changing gaiter and track rod end, replacing wheel and polishing headlight. 10 minutes to get to stage of removing domed cup and o-ring. Got hand around the back of the pump and found that the bolts holding the back plate on were only finger tight....... Then was decision time. Do I just tighten up the bolts and leave at that or do I replace the o-ring anyway?????
I decided, in my divine wisdom to change anyway. 10 seconds to get the plate off and o-ring out and changed for new........... 3 hours Friday night to attempt to get the said backplate back on with no success!

Come 10 o'clock, with a knees that I could no longer feel from the kirb side, ribs that felt like Iron Mike had given me ten rounds of his best, and missing skin and swollen knuckles on both hands I retired indoors with my deflated ego and a bottle of Merlot!
Set alarm for 7 Saturday morning and out for round two! After a bit of jiggery I got them in! Neighbours must have thought I had won the lottery by the noise I was making outside!
Anyway, just made the test centre and got the magic green piece of paper that gives the bongo another 12 month license to roam
However............. all still not good. Firstly, although I have cured the big leak, I did notice that there is still some seepage from the back of the pump. This is at the joint where the main pump body meets the section that has the injector pipes attached. Secondly, The old girl seems now to be as flat as a pancake! There seems to be no go in her when accelerating. Between 40 and 50, if you engage the kickdown, it drops down ok, but almost like its dropping to second and not third. Loads of revs but no increase in road speed. The change between third and fourth seems to be very close together as well.
Do you think its possible that I may have disturbed something whilst I have had my arms in the engine bay?