Stuck manual radiator valves - soak in dw40 ??

Christina

I'm in a 1908 3 story (30 feet rise) house with a hot water gravity, two pipe radiator system. I'd like to bleed the radiators starting at the bottom floor and going to the top, but many have stuck valves. I read somewhere about pouring a penetrating oil around the valves in the hope of unsticking them. Any suggestions for the type of oil to use (wd40 or what). I worry about the oil getting into the water system and screwing it up. Is there something that would loosen it but disolve in water (like KY jelly)?? P.S. This is an ancient system that works well - ideal no 12 oil burner (cicra 1930's) converted to gas (1960s), gravity two pipe system, expansion tank, Honeywell l4006 aquastat and a honeywell motor (I have no clue what it does). Everything works except the house thermostat so we use a mster on/off switch for heating. But that's another topic.. Thanks in advance. P.S. I am new to all this so bear with me..