Vodka- ounce for ounce it's the cheapest solvent available up here, even with the government taxes in. Seriously- just a little squirt of methyl hydrate, gasline anti-freeze or lock de-icer does the trick to get a frozen lock unfrozen- then make sure you apply your favourite lock lubricant when the weather is above freezing to replace lube flushed out by the de-icer. My favourite lock lube by far is made by Slick-50. I wouldn't put their stuff in my engine, but their lock lube is fantastic. Keep in mind that no lubricant will keep a lock from freezing when it rains and then freezes.

Dave

1976 White 300D W115 "Pearl"