420s were known for timing chain problems. Haven't seen nearly as many 560s or 380s for that matter with broken chains. Hell, one of the 420SELs I had, an '86 with 86K on it had the chain break, causing the #4 piston to hit the valve so hard that it scored the bore in the block. Engine was basically junk after that, as MB does not recommend re-sleeving their blocks. I sold that car since I had no time to put an engine in it. The other 420SEL (which I still own) also had the chain break at 102K. I redid the engine (block was ok) and she's as good as new. But, you know, for $15 grand, you can get one helluva nice 6.9!