Hi Glenn,
I did clean them first with sewing machine oil. I had been gently wiping them with sewing machine oil before I read this.
What I've been doing is dipping the rag in the linseed oil, and then just barely touching it to the alcohol.
When that started silvering one spot, I also tried oil + a tiny dab of shellac. That worked better in one spot, but the darkest/crackliest area on the front doesn't seem to want to lighten up, and even going very slow, mostly oil and the tiniest drop of alcohol or shellac, I still got a bit of silvering on one section.
I'm going to continue rubbing mostly oil and a bit of shellac to try to protect it. I am pleased with how much better the black areas look, that's for sure.