I had looked into this topic DEEPLY many years ago when I had my Dmax/Alli with AAM 11.5" axle.
Always go directly to the source!https://www.eaton.com/us/en-us/catalog/differentials/mlocker.html
The G80 most certainly has clutches ...
" Utilizing a flyweight mechanism and self-energizing clutch system
Here's the unit in a video; great explanationhttps://www.youtube.com/watch?v=ftyJvIO0DZ8
Note they call they clutches "active friction disc" and such ...
The G80 requires a fluid with friction modifier, pure and simple. It is a clutch-driven limited slip unit. The reason they call it a "locker" is because it uses a fancy flyweight system to "lock" the clutches (essentially by just clamping down tighter on the clutch pack) to increase torque bias. The unit is ALWAYS in a LS mode; it only "locks" when a preset amount of wheelspin causes the clutches to lock up in a tighter grip. Hence, it's a fancy version of a LSD. And it needs some FM to work correctly.
There is an old document from GM that states to NOT add FM to the fluid. This is a misleading statement. They (GM) sell their own diff fluid (affectionately known as "grape juice" because it has an odd odor of grape juice) and the over-the-counter product already has the FM in it. And because it is just as bad to have too much FM as it is to have too little FM, GM's position is "don't mess with our fluid; don't add FM". But it's really a matter of viewpoint. They are telling you not to add FM because they already add FM to the bottled product. What they should be saying is "Don't add any more FM; we already did it for you." The GM part number for their lube is 9986115. If you search old documents about it, you can read more. Amsoil even came out with a document a long time ago explaining the whole FM topic regarding GMs product, but I cannot find a copy of it at the moment.
If you use diff fluid in the G80 that has no FM whatsoever, you will get clutch chatter and nuisance locking. Adding about 4 oz of FM to the fluid will be a decent place to start. Then add a tiny bit at a time until those nuance and chatter events go away.
More than a decade ago I had a email conversation with an engineer at Eaton about this differential. I would told that all it needed was a GL-5 lube in a typical grade (dino or syn, 75w-90 up to 140 grade). Add in some FM if the fluid does not include it. Done.