Tks for the answer Chris. I have shown my mosfet to a friend of mine (electronic officer) and he told me the same. As inspected mine, exactly the same part failed so l have ordered some spare parts from ebay and will replace it soon. In the meantime l have contacted ares and they will send me 2 MOSFETs for £35 posted.
For the other users of this platform: l burt mine on a skirmish day, playing 2 hrs with a 11.1v Lipo only semi (was cqb) and when my battery died l have switched to a 7.4v lipo battery and after one more hr, the mosfet died.