Thank you, Ed and Gingernut, for your helpful guidance.

I am most envious, Ed, of your 1911 Standard - and its power. I would love to see it and, indeed, fire it. What sort of accuracy does it deliver?

I visited the expert, suggested by the gunsmith today. He made some interesting comments:

1 Lubricant: He said there was no need to introduce Weboil or any equivalent these days, into the air chamber, as all oils create dieseling to some degree or another. He gave me a small tube of 100% pure silicone oil (core-rc.com), actually used for the car racing business (and expensive at £15 for 60mls). Some three to five drops were to be introduced after every tin of pellets.

2 Tap Loader solution if leaking: he said a new tap would be expensive to buy and fit. A better alternative, he said, which will work as well, is to dismantle the tap, place tissue in the centre hole, and spray on an aerosol external chain lube, then restore the tap to its position. This lube sticks to the surface - as it would to a chain saw, and will seal the gaps 100%. As an afterthought, however, it then occurred to me that it might also seal off a section of the air from the chamber if the tap-loader rubs against the exit hole from the air chamber. I might call him next week to seek further advice on that.

3 He also mentioned that it was good practice to fire the rifle with the tap loader in the upright position as it helped to mould the piston seal to the end of the chamber.

So, no doubt, a controversial approach and I thought it worth introducing this as a new thread on this site, so others can benefit and/or debate the merits of this advice.

Meanwhile, I would prefer to have my BSA Standard inspected by an expert but, like others, I still need to find one!

Regards
Andrew.