To seal the toobs internally with a toob sealant you have to be able to swish the boat aroud to ensure even coverage. The sealant goes inside the toob and then you get to tip the boat from side to sde and back to front to make sure the sealant has covered the target area.
Old tobs are a bummer if the top layer of the hypalon is peeling off you probably wont fix it If it has to be abraded off it will be fine.
Going over an old patch is never going to work well get it off and put a new bigger one on. If a rib gets punctured ffshre the repairs are time critical (4kan hour downtime) so i've developed some pretty nifty ways of fixing toobs quickly. to get the boat back in the water and then fix it overnight properly.
Sometimes this means that a puncture leaks a little but just needs blowing up a bit. If I don't want to take off the tube I put a patch of thin rubber on Latex neck seals sort of thickness and work it in well with a wooden spatula. I then put a proper big overpatch on once it's proved to be airtight. I don't like doing it as I view it as a bit of a botch but it works
I have some sealant in the shed which I think I bought from Ribshop, who is a member here