silicone oil on synthetic washers, anything else will diesel. polishing the tube will help as well. LT2 on metal to metal contact and don't polish if you can avoid it as the grease will slide off if the surface is too highly polished.
That said all my webley pistols get a drop of motor oil and fired regularly as God intended
"But we have our own dream and our own task. We are with Europe, but not of it. We are linked, but not comprised. We are interested and associated, but not absorbed."
Winston Churchill 1930