It is hard to learn from your comments, any details about problems - and reports about conditions of your engine components ? With perfect parts there are no problems with sealing, but with typical Vincent old parts you want some seals able to cope with poor faces.
Cracking alu washers in Dowty type seals appear to come from overtightening them. You don´t deal with fibre or all metal seals, you just do them up almost just finger strength. The o-ring inside will prevent loosing the lot and more force does not produce a better sealing.
Vic
One set went on an all new engine with beautiful new caps.
The other set went on a very old engine.
The problem seems to be- the width of the cap flange is correct for the fibre washer that it was intended to be used with.
There isn't sufficient width for a decent amount of rubber plus a strong Al surrounding ring. The Al ring is very narrow and not strong enough for the job.
The seals at the rocker feeds consist of a stainless ring with trapped o ring under the bolthead and an aluminium crush washer between the oil line banjo and the head.
Unfortunately the hold down bolts are very short and only go in for a few threads. This much holding power is more than enough to make the original fibre washers seal.
I eventually got all of the Al crush washers to seal, however the strain on the threads was much too high. Long term, I could see this causing big problems.
I had good luck with the Videan system for sealing the pushrod tube tops, first time around. They sealed perfectly.
I recently had the heads off the one bike for inlet valve seal replacement. That's back together and the Videan seals are still in there. At the moment one is leaking, so perhaps they are not intended to be a re-useable seal.
If so, we'll blame that one on the frugality of the owner!
I also used the Videan seals on the oil supply banjo at the bottom of the engine. They also worked well but they did require a very tight bolt to seal.
I replaced them with Dowty washers and those have been great. They are cheap and easy to find so I will replace them if the line has to be removed for some reason. I've switched to the drain bolt type banjo there so that should simplify things.
Glen