Quick update.
I contacted the manufacturer and they are more than happy to send out a replacement breech :)
I DID find a way to get a badly misaligned breach like this to seal correctly.
Basically I cut a seal from a piece of SOFT pipe. This pipe had a I.D. that matched the O.D. of the stock (upgraded) breach seal. this made a nice sandwich and sealed things up nicely.
If anyone is interested I can take a few pics.