Hi Nigel.Thank you for this site as it helped me very much in quickly finding the fault and correcting my KN7000. I have been talking to my engineering friends as to the reason for only using the genuine part,Panasonic in its wisdom tend to run the components slightly hotter than other companies. The generic part has a lower working temperature and as it is not mounted on a heat-sink this alone would shorten it's life, also the KIA7915PI has an insulated body where the generic parts do not and also use the heat-sink tab as a secondary connection(ie: poss out or ground) In the case of the KN7 there is no room on the board for a heat-sink but even so an uninsulated tab could in certain instances short out or cause other problems.
regards John.