Let me say sorry first, as this does not refer to my Maserati, but as it is within the Classic section and I thought there might be some information with reference to the subject. In addition to my 4200 I also have a BM 850 CI, which I have just put in for service and MOT, it has been intermittently firing on only one bank of of the 12 cylinders, problem being the cats are blocked. I have bought and given to my local BMW indie a new set of cats, not OEM, obviously because they are 7,000 £ a set. But after reading the info on the cats it says not approved for Type approved vehicles, is that a big deal or not. Or should I just go with it, forget it says that, and save six grand. To be honest if I went for OEM parts it would make it uneconomically viable. So I suppose I have answered my own Question, but out of interest what are the implications.