Later cars like my 51 Mercs have a cloth reinforced rubber strip but it is recessed in the gap of the rear quarter and the front grill opening panel far enough that you really have to look at the gaps to even see the material there. If it was intended to be seen by the OEM, it may have been the cloth doped with pyroxylin so that paint would stick. If that is the case, you can use cloth tape and buy some nitocellulose aircraft dope from Aircraft Spruce. They also carry the cloth tape. You would make a mess doping the cloth on some wax paper but it could be done.
Kerby