Guys I am now a fully fledged member of the " I cracked my firebox Club" Whoop whoop.
I had already done around 4 cooks this year when I decided to give my firebox a clean out(I used briquettes for a cook and didn't like the taste so wanted to remove all evidence in case a fellow guru popped by and wanted to inspect my Joe). Half way through cleaning and I notice a crack 3/4 of the way round through the air holes. So I did what so many of you have already done and contacted KJ UK(Grakka). They took my details asked for a few photos and sent me another one out within a week.
Yep I'm as happy as Larry. Thank you KJ