The entire striker is now available at Pelican Parts for $13 each. For what others paid for just the insert and shipping, in the past, I would just go with new strikers.
BTW, I would order a few screws as well, especially if you live in a rust enhanced area. The screws seem to be made of very soft metal.
1979 Mercedes-Benz 240D Base Sedan - Bumpers, Doors, Latches & Lids - Page 2