I just purchased a new, old stock Starrett 436RL-3 micrometer on eBay. It arrived yesterday and externally it is just like new. The fly in the milk though is that the thimble doesn't turn!

This really was a shame because otherwise externally the mic is in very good condition. It was stored in the original packaging which was a plastic bag/sleeve in the factory cardboard case. Apparently it was in a humid location and the threads are rusty; very little rust on the outside. It will not turn or budge at all. I have contacted the seller and he is refunding my full purchase price. I didn't pay very much for it but I was hoping this would be a good one to add to my tooling.

Now, my question is, what can I do with it? I have not tried to force it other than trying to turn it by hand. My first idea is to soak it in a penetrating oil such as automatic transmission fluid for a few weeks to see if that will help to free it up. I'm looking for suggestions to rehabilitate this mic although I don't know if it will still have precision if I do get it turning again.

Thanks in advance for the advice and help I know is coming.