I don't know if you know of the old trick of using coca cola.I unseized an old tractor engine that had been left in a field for 18 years and was full of water you can only guess how bad it was??? take the head off and pour plenty of the stuff in on top of the pistons so that it can really get to work It really is very good, leave for a day or two and work engine by hand back and fore until released, repeat until free.
Use only coca cola not any cola as it doesn't seem to work. (this is not a joke)you'll be amazed.
colin
March 2011