Fortis 400 dual crown... compressor?

[robdavidson]

Ive recently acquired a Fortis 400 dive watch that is actually in pretty good shape given its price and initial appearance.  It has two crowns, the 2 oclok one does the obvious things.  the 4 oclok one however, is less so.  This is partly b/c this crown/assembly wobbles and is certainly damaged.  Looking around the interweb one discovers the supercompressor watches, dive watches with internal rotating bezels.  Looking to the inside of the case there is no obvious mechanism, but, there is an internal black bezel (in addition to a normal rotating dive watch external one- removed in photo), which is rotated about 4 minutes to starboard...  and  I cant rotate it from the inside like you might a decorative bezel ring.  Also, the supercompressor watches ive seen dont have internal and external rotating bezels, perhaps this is an anomaly?  The crown in question also has a center "button" that does not rotate but does move in and out slightly with pressure, the outer (gripping) portion of the crown moves all about with little effect.  Or could this be a helium relief valve...?   Theres not a lot of information out there on these watches.

So is this a internal rotating bezel?  How do I get it apart for inspection/repair?  There is a small pin evident directly inboard of the 4oc crown which is normally concealed under the bezel - drill it out?  I also havent removed the crystal although I sanded and buffed it to a pretty transparent effect if I must say so.  Its quite solidly attached as two thumbs wont dislodge it.    Anyone have any experience with these or something similar?