Go to event list, the one instead of season play and you can just scroll across to them, they are the 100K+, 30+ lap ones.
S class is at Sebring, full circuit, worst track in the history of things that need tracks, I'd rather race my Reventon underwater, in a volcanoe, while getting head from a pirahna.
oh and some cars don't carry enough fuel to make it all the way...My GT2 started to sputter on the last lap and I had to go as far back as I could on rewind, chuck a u-turn and pit. I had just finished the previous enduro without stopping. I was near a minute ahead, won by less than a second.