Sealing tail lights - water leak

[Dave C]

Water is leaking into the trunk and I think it's from the seal between the
tail lights in the trunk lid.  This is a 1987 Audi 5000.  I've re-sealed it
twice already using 3-M strip caulk 08578 but the leak seems worse than
ever.

I figure either this caulk is the wrong thing to use, or else there is a
crack in the tail light which I didn't notice.

I'm tempted to try re-sealing again with the Audi specific sealing
material.  It is p/n AKD-497-010-04-R10 (not sure about the last three
characters in that p/n).  It costs about $60 for a 10 meter roll.

Does anyone know whether there is a significant difference between the 3M
and Audi sealing materials?

Dave C.