Firstfives.org

Removed all the 8mm sheet metal screws. The lower front (stone shield) panel, under the bumper, was joined to the upper panel with what looked like a bead of Mortite caulk. Nice and round between the two parts, with a sealing strip between them.

Not shown on realoem.com, of course. Any experience out there with what the stuff is ? Obvious it's to keep water from getting between the two panels, and paintable.

Unless we just use black silicone or roofing caulk (on a black car ).

Not sure what it is exactly, but you're going to play hell trying to match it. I would not use silicone as it's unpaintable, I would probably use one of the polyurethanes, but not silicone. I feel like I have a pretty steady hand, but...

I think that was seam-sealer. My M535i didn't have it but my '75 does.

It is seam sealer.

I watched my body guy as he replaced the front clip. He used seam sealer for the joint. Then he 'melted' the stuff with lacquer thinner and his finger/rag to form a smooth transition between the two pieces.
Very slick.