Was on AA87 LHR-ORD, a 767-300 (do not have the tail #.) Shortly after takeoff, the captain come over the PA and announced there was a failure to retract one of the leading edge slats after takeoff, so we would circle, dump fuel for a while, then return to LHR. Landed about 30 minutes later a bit fast and heavy, but a really good landing with some serious thrust reverse. (Will try to post vid later