Re: I think..it's the air getting hot during pressurisation by Concorde driving into it,"
"Concorde was surprisingly like the SR72. Both grew and both leaked fuel on the ground. However I don't think the Concorde designers needed to use it as hydraulic fluid as well."
Are you sure the Concorde leaked fuel? I can't find a reference to that, and it seems unlikely that a commercial aircraft would have been permitted if it leaked....