2004 SL500, 1993 S420, 1990 420 SEL, 1985 500SE, 1994 Toyota Supra Aerotop
It does exist! I've just purchased a heavy-duty chain guide for my M117 from my Mercedes parts specialist. It's CNC machined green plastic and much, much thicker. The price was pretty high but for peace of mind it's worth the $90. I'll post a pic later today. Apparently you only need it for one of the guides, the one that fails the most.