Thanks chaps!
Lee, your universal poppets look really useful; if you try to replace these things like-for-like, the various types are a mine-field and not cheap either. They'll be even more attractive if one can't replace the rubbers on the cornelius type.
Masterosouffle, it seems to depend on specific cornies really, though in general more of my leaks are from the poppets than anything else, followed by the lid seals on some of the more dented cornies. I've not had many leaks from the post/disconnect seals or dip-tubes as I replaced any that looked dodgy, but I have had a small number from the PRVs. The poppets are possibly the most frustrating for me; you can often get the troublesome ones to seat by poking them a bit, but sometimes leaks seem to occur later, and the ones from the product side are especially messy/annoying.
My seal failures are usually because the rubber is finally getting too old - hard, cracked and/or miss-shapen. When trying to force-carbonate several cornies at once for my christmas/new-year stash I had a few leaks in a row - which included loosing a new pub-sized cylinder of gas overnight and having to clean up a load of beer; I decided then that the cornies aren't really working for me, so i'm going to try overhauling all the rubbers on my kegs pre-emptively rather than wait until its gone wrong. Aside from the poppets issue, I've got new softer/silicone rings for the lids, new rings for all the posts and dip-tubes and I'm probably going to try glueing new O-rings or rubber disks onto the PRV inserts - its possible I may be foolishly mending things that aren't broken but we'll see.
Barneey (thanks for the link too BTW) I could probably have spent more time on them myself really. Norm advised me not to routinely strip the posts so generally I've only done so when theres been a problem. I can see the wisdom in this as the rubbers do seem to have become moulded to their specific location over time and disturbing things or mixing them up can definitely cause issues, but I'm not convinced it isn't a bit of a fudge - if the rubbers were in good condition then ('IF' you keep track of re-matching the different types) it would surely be better to clean them properly and/or keep an eye on their condition.
Fil yes the poppets are a key weakness for me, but I too have not seen any refurbishment kits for them. Probably its because there are just so many confusingly similar types and only a few are actually designed to take O-rings. The O-ring sizes I use are largely gleaned from other posts/people on here - for the poppets that do take them BS008, the external post ones are BS111, the lid are 417 and the dip tube ones 'were' BS804 - however the latter disagrees with the aussi page you linked to; mine work but I would say their #109 (which is slightly chunkier) would be a better match. The lid ones I got are silicone (from
here, as this is a less common size), which I'm hoping being both new and softer rubber will help those cornies where the mouth is less true than it once was.
Cazamodo That sounds similar to the ones I'm having issues with. I didn't realise until I found a yellow one (most of mine are black), but there actually is a rubber as well as the poppet's plastic bit (that seats the spring), but its a flat thing with a small hole in thats specially made to fit. The 008 o-rings I have can flop around that shaft; I'm thinking of trying some smaller ID O-rings in case that helps but I measure the shaft to be around 2.7mm diameter whilst the smallest O-rings I can find (that would be fat enough to make up the required OD) are 3mm ID so there'd still be some slop. Maybe a pair of rings one inside the other could work but an additional issue is that I don't know if small ones would stretch enough to go on over the poppet's head; the AEB style poppets can be disassembled as their bottom/foot/leg plate is only held on by a crude bayonet thing, but the corny-style ones seem to be fixed more permanently together.
Cheers
Kev