....Naughty Lockheed had a weaker outer wing structure to save weight and a bunch of accelerometers - not territory to hang a refuelling pod off.
Of course NOBODY knew this when the RAF were politically saddled with the wrong aircraft. Had they used Lakers DC10s, there wouldn't be the need for new kit yet...
Actually the L-1011 TriStar wing is much stronger than the DC-10 wing. The DC-10's outboard aileron has to be nulled in cruise to prevent over loading. While the 1011 not only has a full time outboard aileron, Lockheed was able to increase the span on the -500's for improved fuel efficiency.