some more thoughts, and one other thing

The other thing first... the raw water pump was also dripping pretty badly, so that'll be another job as well... a bit of googling suggests that it might be serviceable my your truly... and if not, then a replacement is £200... another thing to think about... how much exactly should I spend on this engine, before i'd be better putting it towards a new one!?

Also... the one thing I didn't do was check the oil in the injector pump... might help?