You might try a liquid other than wd-40 or liquid wrench.
My favorite used by a few machinists I have known(i thought it was BS, but it works) is ATF fluid cut with a solvent.
50/50
Acetone works well.
If not re-using the studs(next time you try this) apply the ATF/acetone mix, hit the head of the stud with a fair sized hammer.
Hit the top hard, but not with a gorilla swing.then use either a pipe wrench, stud extractor(proto/craftsman/etc) at the base of the stud.
A proper stud extraxtor is like a odd looking socket for a 1/2 or 3/4 drive(i'm sure thay make smaller, but those sizes can take some good torque) It grips as close as possiblt to where the threads start to minimize twisting of the shaft.
The item#92502 at the bottom of this link is what I'm talking about.
http://www.sjdiscounttools.com/cutting-threading-stud-extractors-and-bolt-extractors.htmlnot suggesting you but that one, there are better and worse models, just don't buy the cheapest ones you can find they can/will snap apart if poorly made.
I have removed many studs this way out of various machinery and engine blocks.
I use heat when they prove stubborn still as a last resort. Heating the case would be better than the stud as others have pointed out. When REALLY screwed, put dry ice on the stud prior to heating the case. (USE GLOVES FOR THIS)
And at last resort using some metheod of extraction by drilling and a (square ones are better than the spiral ones IMO) easy out type remover.
l8r