Amalgam, solder!!!!! there's newer better products that will do the job. I've used Loctite liquid metal in various applications in conjunction with Loctite cleaner and prep. There's a couple of different liquid metal products, the two tube epoxy liquid metal the one I have used. The colour is grey so will more or less match the chamber colour.

Once the pit is filled and hardened, a piece of dowel with a wrap of fine wet and dry paper will smooth out the filled pit.