Hmm....thanks to you both for the advice.
I am not the most mechanically minded individual you will ever meet but I would like to know that I can repair small/medium problems in the engine if only because of a need to be self sufficient.
Have a very good mechanic on hand, so will probably get some advice from him (when the bugger comes back from his latest cruise) and then see how much I can do myself.
The pump is not noisy so I'm thinking just gaskets but the yard owner did comment on the small flow of water coming out of the exhaust last time we slipped. On the other hand the engine has absolutely no over heating problems. Yes I spotted the blockage fairly early on, the exhaust note is a dead giveaway, but we did not overheat the engine itself.
The oil leak itself seems to be coming only from the seal that is between the main pump and the impellor housing. It's not a huge amount that's come out, a thimble full or two is about all. Made absolutely no visual difference in the sump level.
If the thing does need a rebuild then I'll probably put on a new one but will rebuild the old for a spare and to get the experience.
ps - pump is on the front of the engine block. Working from impellor back it is the first seal but if it leaking then there will be some oil undoubtedly getting into the impellor housing and therefore coming out the exhaust which is not good.
“Life is a trick, and you get one chance to learn it.”
― Terry Pratchett, Nation