Thanks for all your help and quick responses!
I had the opportunity to shoot with someone who had the M2 12 gauge, and we compared forends ( luckily I brought just my foreand). I saw how the O-Rings were installed.
I had the dealer report this issue to the Benelli distributor, and in the meanwhile, I ordered a set of rings from Freedom fighter.
As a side note:
It appeared to both of us that the forends were identical (minus my missing parts). Is this possible? Are the forends the same for both the 12 & 20 gauge synthetic shotguns (both with 28” barrel)?