Thanks JWA.
So the plot thickened a bit, but I am now leak-free. My '95 Club Wagon Chateau has the spacer ring bonded to the factory mirrored glass. The studs are "made" into the spacer ring. I guess this is the encapsulated version you mentioned?
I was unable to source 3M Window Weld round in the 3/16". Can't see that they offer it at all. I purchased more 1/4" round which has been referenced in multiple repair postings. You are correct, great care and a slightly bigger physical gap results between ring and body with the 1/4". It was easy to route the butyl ribbon into the pre-made track in the spacer ring on the body mounting side, and follow the cutout around each stud.
What I discovered is in addition to some of the original window weld ribbon dry/rot, the bond had failed between the glass and the spacer ring at two of the top stud locations, and only on this one window. You can see a "pull gap" between the ring and the glass, where my pencil is pointing in the prior picture. I was able to slip a putty knife through the gap. I determined the bond wasn't easily separated, or replaceable with the window weld, since there was nothing to sandwich the ring to the glass, other than the factory bond.
My theory is that this window may have been installed at the factory, soon after the encapsulated glass was bonded, maybe the ring was not cured and the stud pressure pulled the ring, deforming it at the glass? As the vehicle aged, the bond finally gave way at the physical deformity.
I cleaned and dried the gap, air and visual checked the rest of the ring/glass to be good. I then inserted 3M trim adhesive into the gap and clamped the ring at the two questionable studs. After verifying that repair was good, I then layed a bead of the Permatex flowable silicone at the corner of the glass-to-ring connection point as an additional step. Maybe overkill, maybe temporary, but other have reported multi-year success using the Permatex alone. My hope is the re-bonded ring at those two adjacent studs, along with the extra steps will make it a good repair for some indefinite period of time.
Re-installed glass, (careful here folks...like JWA said, just light snug by single hand with a nut driver
), cured, water tested tight, and still dry after washing, and multiple fog sprays in the window areas.
We'll see how it goes. I guess the only other solution was to try to find a new window with the ring bonded from the factory. Bet that would cost a bit to get one with the right mirror tint to match the rest of the vehicle.