You don't actually stake the castle nut, you stake the endplate to flow metal into the cutouts on the castle nut.
If the castle nut shatters it most definately isn't mil standard and would actually be in the same league as Jennings/Bryco/Raven standards of pot metal.
In my most humble opinion, if anybody really needs to goop Loc-Tite on the extension tube to keep the castle nut secure then they have some real issues with quality standards.
A properly dimensioned extension tube-castle nut-endplate that are properly torqued will stay in place without the staking or the Loc-Tite.
There are lower receiver blocks that fit in the magazine well and allow the receiver to be chucked up in a bench vice available.
Great piece of tooling.
I also have a heavy duty, multiple use combination wrench from Smith Enterprise that I normally use to break extension tubes free from the lower receiver.
Use caution, If the extension does not pop free using a moderate amount of force you need to switch to a strap wrench cinched up tight at the end of the extension tube close to the receiver through ring.
Remember, counter clockwise to loosen and clockwise to tighten.
If you try grunting the too tight extension tube off using a wrench at the end you run the risk of bending the receiver or breaking the top of the receiver extension through ring.
Heat will cause any Loc-tite to release but you will have to get the area really hot, 400 to 600 degrees farenheight depending on the type of Loc-Tite.
A propane torch will do the job.
Don't replace the Loc-Tite on the rebuild, the fixed stock will keep the extension tube in place just fine. HTH