Sorry to hear the bad news, Nanuq. But you had a good run.
If I remember correctly, with an MBW 1665 I think you need to go gen.
Insert a small, triangular hobby file into the tube until it grabs the tube's inside walls, then unscrew. In some cases, the tube may have been cemented into the case. If you heat the case with a hair dryer (Ms. Nanuq can probably help you with that), the tube should then unscrew fairly easily.
Depending on the condition of the threads in the case, you can either just blow out the debris & screw in the new tube, or you may need to use a tap to redefine the threads. Most of the watch supply houses sell the Rolex taps (you need the larger of the pair for a Triplock tube). Everyone has their own preference, but I always apply a small amount of GC crystal cement to the tube's outer threads just to help with sealing (Rolex specifies no cement or sealant in their service manuals, so this is definitely optional when fitting a gen tube) & then screw it in until snug (not too tight).
The process is actually easier to do than to describe.