heat is good to get the oil into the joint, but it doesnt have to be red hot, just hot to the touch, and capillary action will pull the oil in as it cools.
I used to restore redwood water tanks back in the 90's. some of the iron bands were over 100 yrs old, outdoors that whole time. we'd heat em up and squirt em with diesel fuel and let em cool off, several times if need be. and almost always they would break loose. torching off the nuts was a last resort we didn't use often because we didn't want to burn the wood or have to weld new all thread to the rusty old bands.