Thanks for the advice, unfortunately the previous owner wasn’t the original owner either, so doubt I will get anywhere with a warranty claim.
It may well have been there a while. When i picked it up i did look over the area but there was nothing to see with the paint over the top of it and it still had the bottom bracket in too. You could tell it wasn’t a fresh crack, there was already a fair bit of grime in there.
What did you do with your in the end timmys? Did you carry on riding with the crack or bin/repair it?
The rest of the frame looks in very good condition for its age, so if i could repair it and have it last another year or two atleast that would be good!
I’ve seen that welding video before, i just wasn’t sure whether it would weaken the other welds around that area? I don’t know if the frames get heat treated from new?