I often resort to heating fasteners to loosen them, sometimes combined with penetrating oil. Heating them with a torch might allow you to burn the goop off too so the oil can get at the threads.
However, you have to be very careful and this isn't something I typically try on body metal, or on things I need to reuse. Works great on exhaust parts though.
Depending on the access and your tools, you can also drill out the center of the fastener. Sometimes you can get the walls thin enough that it will crush or at least deform enough to break loose. I often do this on delicate areas, where I can't risk damaging the surrounding material and I don't care about saving the fastener, but its very time consuming and, if you're too agressive and catch the fastener with the drill, you can sometimes twist the surrounding material, making a bad situation worse.
Personally, I'd try carefully burning off the goop (with a fire extinguisher close by), then alternate heating and spraying WD-40 a couple of times (the oil left on will catch fire with a flame - be ready for it and wipe the surface off first to minimize that.) I'd do all the bolts one at a time, then go back to the first one (since the oil will have started to dissolve in) and try to loosen them. If one or more were still obstinate, I'd just spray some more and go on to the next one. If they still don't budge, I'd spray them liberally and let them sit overnight. Once you've stripped the heads, it'll be a lot harder, no matter what you do. Better to be patient and let the oil and heat do their work. First you have to get the goop off though.