The 1990s Mercedes 'biodegradable' engine harness has crumbling insulation and is a recurring inspection point. Commenters variously bound the affected years at 1992-1995 or 1991-1996, but agree the real determinant is the injection system: CIS/K-Jetronic cars have no harness issue, so pre-1992 300SLs and the CIS 1992 500SL are exempt, while some 1996 cars still shipped with the bad harness.
Biodegradable engine wiring harness and its exact year range
Mercedes-Benz SL (R129) · mechanical