[W126 Coupe] Special paint where tire bead meets rims???

[Dick Spellman]

I've noted that Mercedes uses a special coating of paint around the 
inside lip where the tire needs to seal with the rim.  Does anyone know 
what the paint make-up is??  I'll need to re-apply this coating to avoid 
leaks.  It's seen as a 1 to 1 1/2 inch wide smooth green or red paint 
where the tire bead seals on the inner lip.

Thanks in advance.

Dick