I completed the championship last night, The only assist to keep on is Skid Recovery Force. You will win the first 5 of 6 races in first, and Susuka will suck immensly because you will be wiped out, and guaranteed to spin in the sand or grass one time too many for 12th.
you don't need to rebuild chassis or engine, just oil change, and find a good tune, there is one magical tune that awarded me the gold, finishing each race a minimum of 10 to 30 seconds ahead, even with 1 or two major crashes. search for it in the tuning section. edit, I'll go find it.
Btw, the ticket awarded is LVL21 and not LVL24, I saved the game and will try reloading it a few times to see what I get each time.