I suggest the crock pot and antifreeze method.
http://www.rccanada.ca/rccforum/showthread.php?t=38669
You might also look here:
http://www.rcgroups.com/forums/showthread.php?t=81577
The Crock pot method is generally for gummed up engines but most antifreeze formulas have something in it for rust as well.
Robert