M273 V8 engine character and known weak spots

The naturally aspirated M273 5.5L V8 in the SL550 is praised as smooth and robust, but owners flag an early central timing-chain gear that was reportedly under-tempered and corrected around early 2007, and plastic variable intake manifold flaps that grow brittle with age. There is back-and-forth over oil-ingress-into-harness claims, with one commenter arguing that failure mode belongs to the later M278, not the M273; earlier cars used the 5.0L M113 (302hp).