There's a lot opinion about head bolt problems on 6.3 M156 engines but from what I can see no one has hard facts on the volume of cars affected by it. A quick check on how many left shows over 85% of CL63s are still roadgoing, likewise for ML63s, S63s, C63s and CLS 63s and a look on auto trader shows at least 2-3 63 engined variants (mostly MLS admittedly) have done over 120000 miles,so yes, head bolt problems exist but not to the extent some forum owners imply. Other cars of similar types e.g. M6 are declining in use in a similar fashion ( by about 15% over ten years).....according to DVLA so is it really that wide spread? Before anyone suggests it's a big deal there are over 3600 registered C63s and I can't find hundreds of owners bitching, maybe 10-20 odd and most on US websites. Thoughts?