So I took advantage of a clear day here in Portland (finally!), to remove the manifolds off my block so that I could replace the gasket. All the tips from another post below proved to be helpful. I was glad that the solvent spray I used seemed to have done its work over multiple days of sitting. All the nuts came off after the first slight "crack" sound to break them loose. When I finally came to the very last nut at the back of the engine however, my first turn was much easier than all the prior ones and I was dissapointed to feel the actual stud turning and then slip right out of its hole quite easily.

So... not having experience with such things, am I screwed here? The stud seems to have broken pretty deep, but there seems to be just the start of threads on the end of it. Is there any solution here? I'm praying I don't have to pull the whole block and have the end of the studd drilled out or something?