Well over the yeas I have used just about everything that is made for freeing up rusty things, and IMHO, the best stuff yet is the flourescent yellow dye penetrant spray that is used in welding shops and machine shops to check for cracks with a black light. That stuff is amazing and it works. Just spray the item and allow it to set, and odds are it will be able to be moved. If it does not free totally, apply some more once it starts moving and allow to set a bit again. Some heat helps sometimes but I have found it mostly un-necesary. Cost is about $5.00 a spray can at the local welding supply stores. The dye can get into the tiniest of cracks or crevices and seems to flow right through rust.