No oil will leak past OIL seals unless they are knackered, but will leak past "flat" seals easily.
Cossie oil gets TOO HOT, tests done at a very pretigious US place into oils, showed the ENGINE oil temps to be on AVERAGE, 30C HOTTER than the water temperature of a typical engine.
I am a firm beleiver in(stated) OIL COOLERS, air to air, not the modine ones, the oil temp on my XR4i used to hit 130/140C, without being used hard, just town work, although came down to 90/100 in constant gentle m/way stuff.
I ALWAYS where possible use VITON seals, as these are so much more suited to high temp, than a std seal, as they were made just for this high temp, but are expensive, two cam seals bought last week were £21.03p(inc vat)
tabetha