Have owned BSAs for almost 60yrs and in that time stripped & re-assembled their front forks dozens of times. Never had one leak oil on me until I did my GF a couple of years ago. Just would not stop dripping oil to the extent I gave up and let the forks run dry if they wanted.
Well, today I decided to drop one of the fork legs and take a look. I add that this was - as far as I recall - the first time I'd used stainless fork seal holders, because I'd got tired of having to replace them when they got rusty despite my road bikes never going out in rain / damp conditions.
I'd suspected the oil seal wasn't being clamped properly between the holder and the fork leg, which was proved correct. The thread on the leg is 1/2" max, though only 7/16" is ever used. The seal is 5/16" thick, so it follows the holder recess depth should be close to 3/4" (7/16 + 5/16). It was actually 15/16", meaning the oil seal was floating around unclamped. I turned up some 3/16" spacers to put above the oil seal, and now the latter is clamped normally. Hopefully an end to oil leaks.
Conclusion - if you're inclined to use stainless oil seal holders, best check the depth of recess before fitting. I didn't, mainly because I have an (ill-founded) notion that if I have to check others' work then either they shouldn't be doing the job - or I'd be better off doing it myself. Can't now recall the supplier, otherwise I'd warn members to check their products.
