Thanks gents.
I'd already since decided to buy a replacement Merc mirror casing, indicator LED strip and lense as they are just over a ton all in - I couldn't see any on eBay last time I looked but there were a lot of non-OEM replacements it looked like.
To completely replace OEM, the original price was £500, but the majority of that was for the metal chassis.
As you say Alps, someone else here also suggested chemical metal from Halfords or similar.
It's only that small lug broken off so I am sure I can repair that or fabricate something that will probably be stronger - I'm sure the metal is bleedin' diecast like Matchbox cars used to be (not deliberate by MB I'm sure)...
I need to save some money for my now-exhaust issue.