I noticed that the bolt attaching the boom to the mast wiggles quite a bit (see marked area in image) and I started looking for replacement parts.
Luckily, the number show very prominently:
508-152/-153 on the bracket 528-071 on the metal piece attached to the bracket by a bolt.
What I find strange: All search results for the numbers give me "Rodkicker Brackets". And indeed, a very similar (508-257) part is used on my boat to support the rod kicker. But I'm looking for a boom support bracket.
What part(s) do I need and where to source them from?
When I google 508152 I get a Selden catalogue page of boom brackets - https://support.seldenmast.com/files/excerpts/595-808-E-87-89.pdf
I also got a result from a rigging company listing the part at an eye-watering price of around £750. On that basis, I'd be tempted to consider other ways of solving the problem, perhaps by machining the bottom hole and sleeving the bolt there.
If the pin is worn, replace the pin. If the fitting is worn, which is likely as it's the softer material, fit a bushing top and bottom. There's plenty of beef left on the fitting by the looks of it, no need to replace the whole thing.
On our boat, the fitting for the gooseneck toggle and the rodkicker were identical. In the Selden catalogue the number is clearly listed for the gooseneck though.
Thanks for your input and confirming that there's not some botched job going on And the brackets are indeed similar.
I will probably look into replacing only the bolt or finding an alternative way of fixing up the bracket.