I think I may have found the reason for the problems we've been having with repo updates. Not exactly guaranteed, but I've just been able to go through all the areas and update them without any failures. Hopefully I've got the answer, but, either way, there are some updates available for the first time in quite a while. They're also important, since all of the ones that have just gone up are security related.
As well as the Firefox and Seamonkey updates, there are language packs for them as well. I'm now going to try adding a few new packages and see if the updates work this time......