Thanks for that - It's sort of what I was looking for, but unfortunately it appears that the bolt buffer is missing from this bolt assembly as well.
The buffer would normally attach to the hole in the vertical plate shown on right hand side of the picture. The buffer stops the bolt mashing the plate, which is what is happening to mine.
I can't work out if there is supposed to be a buffer on both sides of the plate, or only on one side. My one has remnants of a buffer on both sides, but if that was the case I can't see how it fitted (the plate also acts as the lock between the upper & lower receivers)