I don't think the taillight seals have any adhesive, I think they are a compression seal. The other weather seals, doors, trunk lid etc, are held in place with contact cement though.
Might be the PO tried to shut out water through the use of silicone or other sealant rather than springing the bucks for new seals.
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72
'02 CLK320 Cabriolet - wifey's mid-life crisis
2012 VW Jetta Sportwagon TDI...at least its a diesel
Non illegitemae carborundum.