If the case tube has splines at the outer edge, always try to remove the case tube with a CT spline wrench or broach first.
When a case tube is stuck and/or cemented in the case, I use a short piece of wire that is a 'light slip fit' into the case tube and heat the wire with a small torch powered by a BIC cigarette lighter. The wire prevents the flame from touching the case, bezel etc. and still heats the case tube enough to loosen the cement and break the tube loose.
Remove CT gaskets, crystal, and movement first.
There are many versions of these mini-torches on eBay etc.
If the case tube has splines at the outer edge, always try to remove the case tube with a CT wrench first.
You can sometimes remove a case tube by jamming a six sided tapered broach (or small file) into the tube and unscrewing it...or you can broach the ID of the case tube until all that is left are the threads and chase them out with a pointed tool....but you have to be VERY careful not to cut into the case threads with the broach.
Genuine Rlx 6.0mm and 7.0mm case tubes use the same tap size...3.0mm X .35mm (3.0mm diameter with .35mm thread pitch).
Later sapphire DJ etc. have 6.0mm crowns with 5.3mm case tubes and use a different case tube tap...2.0mm X .25mm (2.0mm diameter with .25mm thread pitch).
Tapping or re-tapping case threads is a HUGE hassle. Trouble usually starts before the tap has made one full revolution because the tap is not started straight and it binds up...or breaks.
Don't ask me how I know this.