Your load calculations look correct.
The transformer temperature rise of 65C is based on the interior of the center coil winding, theoretically the hottest spot in the transformer.
If the "surface" of the cooling oil was at the same temperature as the windings then very little heat transfer would be occuring occuring.
For a typical liquid filled transformer the temperatures are:
ambient = 40C
average conductor rise = 55C
hot-spot gradient = 10C
Total permissible ultimate temperature = 105C
