I often claim to be a child of make do and mend parents, as I suspect may be the majority of UK baby boomers, thus self reliance of the type I learned, and the modern world do not fit well together, however I have removed many a seized brake nipple using a technique that is FAR from recommended, if not life threatening to those who might be strangers to a tool kit...Also being somewhat forgetful in my old age and having made many mistakes anything I type can be entirely wrong..YOU HAVE BEEN WARNED. Brake fluid and WD40 are flammable.
For many a year I had oxy acetylene welding kit in my garage, and when calipers were just bare cast "iron" lumps, directing a narrow ( thick pencil lead) welding flame at the location on the casting where the bleed nipple threads would run internally till it glowed read, then applying as much pressure on a preferably hex spanner as is reasonable to exert on a bleed nipple, chances are it will come out. I have been known to apply a bit of pressure back and forth. as if to tighten before loosening, to assist the start the release process, or at any time during unscrewing if things tighten up a bit... though the application of a little more heat can also do the trick if you have not already extinguished the welding torch..
The thing about a welding torch flame is that the searing heat builds quickly in the area of the nipple and the density of the casting of the calliper is such that it does not transfer that heat to the extent that it damages the rubber seals, I have never used a blow torch or anything similar which may assist the process, but risk spreading the heat wider and taking longer before a nipple might release if at all, as to the possibility of of damaging rubber seals ..???
As the normal design of a brake nipple to caliper fit is that the sealing is performed by the "pointed" end of the bleed nipple fitting snugly into a countersunk drilling at the base of the threaded hole in the calliper, it is unusual for that to leak, though not impossible if a the remains of a sheared off nipple may have been bored out in the past and the repair has involved re threading the hole marginally out of line, thus the countersink to nipple fit may not be mating correctly.....?
I had a couple of enamelled, adorned with a logo Brembo calipers on which I broke off two nipples...!!! .Not only am I without my gas welding kit of times past, even if I had it, no way would I have used it on these fancy calipers, thus I sent the callipers off to folk who seem to have a good rep, who did a fast turn around too.. I think it is possible that a caliper with a seized nipple is preferable to work with, than one with a sheared nipple. I have also read where ultrasonics may be involved in some release attempts, which would seem ideal on fancy painted calipers..?
https://pro-calipers.co.ukGood luck in choosing a method that suits.. Just noted that the calliper is alloy... flame time would have to be reduced accordingly. Insert fitting are where it is possible to drill fractionally off line...!