You can save a clean lap which is slower than a dirty one using the "save replay" option instead of "save ghost replay", that way you save all the laps on your last try, including that clean lap you want. And week 155 will not be hopefully arcade mode, it'll be definitely (see post 1).
I had a quick session, and I'm running consistant 17.4's, but I didn't save anything yet. Of course, T1 doesn't count for much, as it's only one corner (or 2 linked corners, if you prefer), and the last sector is much more tricky and we can lose or gain a lot of time here. The setup I got was:
Transmission: tranny trick, auto 1, final 4.400
LSD: 10/15/5
Weight: 0/-50
Brakes: default, I tried some changes but didn't notice anything special
Aids: none
Springs: 15.0/12.5
Height: 100/100
Dampers: 7/7/7/7
Camber: 1.0/0.5
Toe: 0/0 (but I didn't try anything else, so it may need tweaking)
Stabilisers: 6/6
Edit: I just noticed my setup is quite close to Dan's, maybe it means I'm finally getting to understand how this works! However, I didn't drive the way he did: I didn't drift turn 1, so my best T1 yet was 17.39. Actually, I couldn't drift that corner, because the car seemed quite understeery, probably due to having to brake (I'm no expert on drifting), and I can only do the easier drift at the last turn (but I was using 3rd gear, not 2nd as he does). To get a braking point for the chicane, I use the signs at the right side of the track: I brake a bit before I pass the first one.