Silver soldering issues

I think you are on the wrong track here. Vibrators were not originally "silver bearing solder." Let's define this into

"Silver bearing" AKA electrical/ plumbing low temp and

"Silver braze" AKA high temp used to be commonly incorrectly called "silver solder." Used for such purposes as refrigeration tubing

The problem with attempting to use low temp silver bearing solder at all is getting electrical--compatible flux. MOST FLUX (all?) you are going to find in the public / local stores are going to be acidic / plumbing/ hardware use AND NOT FOR USE in electronics

PERSONALLY I would use common lead solder, IE electronics/ radio solder.

I would also check the socket contacts and make sure they are in good shape Heat is generated by poor contacts

On a side note, at my part time job (I'm 69) I am building power wheel chair components and we use "no lead" solder. It is a PITA. It does not flow as well as the old lead based, and is much much fussier to deal with

We do have an additional rosin liquid flux for it which we use for some connections. If you think it will help I will try to get the specs on it. No idea where you'd get small amounts, unless Mouser Electronics, etc