Can not help with leaky bit but
I have a twenty litre port Barrel and some years ago i must of had a brain fade and put a bottle of VP in it to top up or something. any way all went sour / off and i just left it thinking i should do something about that one day. well other day i was going to Rutherglen to get some wine and thought i might as well empty out barrel and clean for new port.
So i tipped out 10 litres of port i had stuffed and been sitting there for about 5 years. i then rinsed barrel about 4 times. (side Note) if you leave plain water in barrel for longer than 2 days without changing it you run the risk of rot and mould.
I then went to Rutherglen and got good tawny from Buller’s. on my travel around i went to All Saints and out the back they have a Cooper The Keg Factory. It just so happened that it was the same guy i brought my keg off twenty years ago in S.A. he has expanded to Rutherglen and comes up for the walk about weekends. Any way i tell him what i have done and with out to much Ridiculed he tells me how to fix it.
Wash out with very hot tap Water.
Mix up 6 Campden tabs crushed per five litres of cold water for barrel let sit for 2 hours.
Rinse out barrel very well again.
Mix up 1kilo of sugar per five litres of water needs to be at about 40 deg.
then add that and 2 packets of bread or beer yeast to barrel and let grow for 5 days.
rinse Very well after time and fill with port.
Do not let it sit around empty fill it straight away.
I just did my barrel and worked a treat.
Only use Tawny Port.
If you can not stop your barrel leaking may I suggest you get new one from Keg Factory they are great people and barring the silly things I have done my barrel has lasted well.
They do not line their barrels with wax or other things so you get great flavour forming.
If you want to have a barrel for rum or whisky or brandy just tell them and they will source the right type of oak and make it for you. ( that’s my next order)