Sorry, don't know anyone on that side of the pond. Dockhead, Atoll, and Boatman on this forum (and probably some others I don't know) are relatively local and might be able to make recommendations.
I did like the suggestion above that it could be the cutless bearing itself holding things slightly out of alignment. When you get the new housing try the installation
first without the cutless bearing in place, that should allow a little but more latitude in alignment. Might even want to try that with the current
unit (if you can get the bearing back out
). If you can install it without the cutless bearing you might want to investigate alignment, or see of you can get a little play in the shaft by disconnecting inside the boat, installing the bearing housing, then re-connecting the shaft.
I only have a small amount of experience with de-zinced bronze, what I have seen is usually quite red/pink all the way through. You might hit the very end of the stern tube with some sanding
to expose a fresh surface and see what it looks like. From the picture doesn't look terrible, but I am not a metallurgist