The Bosch mechanical injection pump and injectors are the dominant mechanical topic; rebuilt or NOS pumps alone have sold from roughly $5k to $46k, with injectors described as increasingly hard to find. A small circle of specialists (HK Engineering, Koller, and independents descended from craftsmen like Hans Utke) is relied upon for calibration and rebuilds.
Bosch mechanical fuel injection: parts scarcity and rebuild specialists
Mercedes-Benz 300SL Gullwing/Roadster (W198) · mechanical