Would you expect the fluid to seep out from there?
Yes sort of..’design feature’ of RS forks of that period (Rev, Pike, whatever…if it had the moco unit it could leak): oil leaks out of floodgate. It was a while back but I’m sure Loco sold me a couple of o-rings that would solve the problem.
Is it easy to top up the fluid in the damper?
Yes. 123ml of 5wt oil as per my RS service guide. Need a 24mm socket
Is this an early warning that the damper is about to fail? (the forks seem to be working better than ever after the service)
No, not really…If you lose too much oil then you won’t get compression dampening so for example if you set the compression adjuster to ‘lock’ position the forks will still move
Have I just been lucky up to now and they are not supposed to be stored like that?
For the foam rings/bushes it good to store upside down but then my old RS forks tended to suffer the problem you have if you do store them upside down!