The Official 356Talk Forum

B and C cars had rear reflectors. Euro spec cars had the reflectors below the bumper. US spec cars had the reflector above the bumper and still had the mounting hole below the bumper. That plug is for the lower holes. Some cars had a chrome screw instead. The plugs for the taillight access holes are nearly flat and about 30mm in diameter. Try International Mercantile.

I know of no welded nut in the engine compartment. Porsche usually used those sheet metal flanged nuts spot welded in place on sheet metal.

I think the correct rubber plugs are rather thin and lay flat.

IM has them. Here is a picture.

Kevin and Harlan, thanks for the help finding those parts.