When new the factory used what was called glazing putty to seal the front and rear glass. It was off white in color. All these year later it has likely hardened to a concrete hardness. When I do front and rear glasses I often have to chisel the old glazing putty out. On a side note, this same glazing putty is was also used under the "A" Pillar chrome trim, as well as under all of the chrome pieces on the soft top and hard top. Don't skip out on renewing the sealant in these areas. Otherwise water ingress and internal rusting/corrosion will occur. This glazing putty was placed between the seal and the opening, and after installation it was also placed between the seal and the glass. That process is still the proper way to do it, but the glazing putty has changed to a black sealant that you put in a caulking gun. It's non hardening, and is still available from Mercedes. Part number 001-989-31-20. If you're a diehard restorationist you can go buy plumbers putty, as it's essentially the same as the original glazing putty. However, it's time consuming because you have to roll strips of it out by hand. Regardless of which putty you use, the rule of thumb is if it's not oozing out after you tighten something down or rope a glass in you didn't use enough. So be generous in the application.
