Hi David, I think this one of those questions you have to ask yourself, how much more is it going to cost to have the full upgrade, against a new engine, if you only have the new tensioners done and one of the other parts fail, it will have been a n even more expense. Could be an idea to go to another dealer for third opinion, what has the garage said who carries out your usual maintenance. I know I have not been much help here, if I was in your shoes, I would have the work carried out, but that could be me just being over cautious, good luck.