I had my timing chain on the 300SE replaced along with a major overhaul. Barely 3 months later it snapped. Fortunately, it was under the workshop warranty, so I had a new set of valves and pistons replaced free of charge.
If you did say its a known problem on the 420, is it also likely that it could be a problem with the 300SE? I mean, a timing chain just don't snap as they like, would it?
126 tailed by a 203, 129 leading the pack.