All great advice! This is my 2 cents all gained from over 40 professional years and who know how many nonprofessional years experience. I was a dealership mechanic and am a retired fleet mechanic for 33 years for a public agency with a very diverse and complex fleet quoted as being “only second to the military”. If it’s a nut on a bolt or stud, heat the NUT ONLY as quick as possible to expand it to remove it. If it’s a bolt or stud in a manifold or whatever it’s stuck in, heat the PART ONLY as quick as possible to expand the part around the bolt. If you heat everything, everything expands and gets soft then breaks off. Also if it doesn’t work be careful when reheating too many times because everything could become welded together. When heating aluminum extra care is needed, too much heat and you’ll pull the threads. Lock Tite secured fasteners need a little heat to melt the product. Again my 2 cents, Lock Tite is a great product when used correctly. Lock Tite on steel bolts into aluminum is not necessary it will usually pull the threads out when removed. About the torch setup, by me if the welding supply didn’t sell you the tanks they won’t refill them. When they’re out of date you will pay for the re-certification weather you own them or rent them. Only high pressure tanks (over 1000 psi. oxy, argon, etc) will need to be re-certified for a fee. Sorry this might have sounded like a lecture but again only my 2 cents. A word about extractors. If the bolt broke off, an extractor will break off. If the fastener sheared off then you have a chance with an extractor. Heat used with extractors won’t work either, they only remove the temper of the extractor and they strip out. Oh one more thing, it seems like some of you have a love affair for the gun (impact wrench). Do yourself a favor, do it by hand, learn how to get the feeling don’t rush you’ll only be spending more time fixing what you needlessly broke. Above all have fun and learn!!