The weld in front of the barrel nut will be where the barrel is pinned to the body as part of the Deac process.

i can only see a WD arrow near the ED logo so can't comment on that. But it does sound like an inspector mark.

I wouldn't worry about the condition, you'd be hard pressed to find anything that's 70+ years old in mint original condition. It just doesn't happen with issued kit.

I believe the Brens were given to the Irish Defence Forces right when we needed them the most. This decision must have come from the very top of Government and so they must have been worried about the Germans entering the UKicon or controlling our waters by invading the neutral country of the Republic. The majority of the Brens are from 1940 and are sequentially numbered in the D series with a splattering of 38s and 39s.