Heat is great for freeing up gummed up parts because it softens the waxed up oil. WD-40 is a great penetrant. The only sure fire way to get old parts free is to disassemble. Especially carbs because you never know if anything has plugged up the fuel passages. Also, cooking a whole engine in a crockpot without disassembling is a great timesaver ONLY IF you run the engine afterward to burn out the antifreeze residue and get oil into every part of it. Engines will rust inside if not run or are not at least thoroughly oiled. Running is still the best bet because it heats up the engine and helps to evaporate the antifreeze. I personally disassemble every engine before I clean them and use a toothbrush to knock off the baked on crud. This way I can SEE if I'm getting them all cleaned up inside and I can be sure that I'm removing all residue and oiling every part.