In defense of CASA if I were in their position and asked somewhat informally if operation beyond the max published 40 degree temp was legal I too would probably say it isn't. What is the benefit to say otherwise?
Just the same as I would respond to the question if it were asked if it is legal to T.O. below 0 degrees as this is the minimum listed temp in the P charts(1978 C182RG POH).
Of course applying common sense you will likely arrive at a different outcome particularly as 40 degrees T.O./LDG is permitted at 8000' PH with a QNH of 980 hpa (same POH)