I picked up this double roller chain the other day. It had sat undercover but outdoors for several years in Eastern Washington, a place that gets hot and dry in the summer and cold and snowy in the winter. It was't 100% frozen, but very close. This chain is essential to the machine - an integral part of the setup for ferrous cutting - and I decided to try the latest thing in penetrating oil. I took a coffee can and put about 5/8" of automatic transmission fluid in, and matched that amount (roughly) with acetone, and submerged the chain and left it overnight. The next day it was better, still unmovable in several spots, so back in it went. The next day (today) it's nearly all broken free. Most of it is swinging loose like a new chain. I'm guessing that by tomorrow it will do the trick.
I read about this in a recent "Machinist's Workshop" article. Says this stuff works better than Kroil, P.B. Blaster, Liquid Wrench, or any other, and for a tiny fraction of the cost per unit volume. I can't verify that it works better, but I'm sure glad I didn't have to come up with about 2 cups of Kroil for a one-off job like this!