For no particular reason I wanted to feel the temperature of the differential on my 230 SL after 60 Km trip. The diff housing was quite hot, one could touch it briefly, but only for a few seconds without getting one's hand burnt. To me the temperature seemed high or is this normal? The diff oil was changed with Castrol Axle EPX 80W 90 a few months ago to the correct level and the diff has no leaks.