At the risk of staring "yet another oil thread", Valvolene sell a VR1 racing oil which is high zinc and a straight 50 weight. Easily available (I get mine from O'Reilly's". Friends swear by it for old wheezers like what we ride. If not on the shelf, just ask for it and they will get it in for you.
I use Pennine Lubricants (I think they are in Sheffield) for all the oils I ever need to use (tractor oils, hydraulic oils, chainsaw oils, two stroke oils, motorbike oils).
That green stuff from Halfords is good if you want to find out where seepage is coming from.
I use a Morris brake fluid oil for my JCB. I have also used their Running-in oil for my M20 and a rebuilt Leyland 270.
Regards
Pat
ps If oil seeps out of the Primary Chaincase, then a) you know it had some in and b) constant topping up keeps it fresh.
