That sewing machine guy does NOT know what he's talking about, and I hope he hasn't ruined a bunch of perfectly good machines. I would talk to the owner (if he isn't it) armed with the manuals from each machine and say he's destroying machines and giving that business a bad reputation. People like that need to be stopped!
The thing to remember is the machines are not new, new information wouldn't typically crop up for them Singer isn't supporting them anymore so they're not innovating for them. The only changes are what people like us are doing, i.e. TriFlow works better than sewing machine oil for the non-motor maintenance required. Oil and grease are not interchangeable. They serve different purposes!