MaJoC the Filk wrote: Now I know what sort of fingerpicks to ask for whenever my fingernails fracture.

Yes. The Alaska Piks literally saved my ability to fingerpick. My fingernails are no longer strong enough to play for a full hour without eroding away. And attempts at a fingernail-friendly diet didn't help. I tried nail-hardening paints; they just chipped off. Artificial nails pulled off. The first fingernail-replacing picks I tried were useless, too. But the Alaska Piks work for me.

The one drawback is that, once you're used to them, it's hard to play without them, because it's almost impossible to make your fingernails be the same shape as the picks!

Regarding petroleum products on the strings: They're very unlikely to damage the strings -- petroleum is not like a salt or an acid, which readily breaks up into ions. It's the ions that damage the strings. That's why it's so hard to get oil off beaches and such -- it doesn't react to the chemicals in the water The problems with it are that it might affect the sound of the string, or soak into the wood -- or just make your hands feel icky. So it's a matter of what you (and your instrument) can tolerate.