Late breaking is the key at Laguna... Also do not over drive T2 (the hairpin) and T3 (the 100 degrees right)... Stay on the inside for T2 (a good passage into 3rd gear with the roadster at the exit of T2 is at 16.6/16.7secs of your lap.) and try to dive in T3 pretty early...
The fast curb going uphill, before the corkscrew is also a key corner... DO NOT TOUCH THE BRAKES there... you got to practice to dive by releasing JUST a little bit the accelerator. A good exit speed out of this corner is at about 88mph... A perfect corner, you don't go under 87mph at all and you touch the rev while slightly drifting it... You need to keep as muhc momentum as possible to climb the hill.
Then late breaking at the corkscrew to dive in directly into it. By late breaking, I mean right after the sign at the very top (2 or 3, I don't remember the number). You need to have a consistant breaking to enter it right away at the perfect speed. You basically let go of the brake once you dive in, to accelerate again right away.
For the right curb/corner after, let go off everything to enter in and reaccelerate right away. With the roadster, there is no need to touch the brakes if you have a good trajectory. Just a downshift into 3rd...
Last corner... well... last corner lol. I hate this one,You need to cut it as much as possible without getting an off track. Diving in quite early is a good solution, though be careful not to re-acceleate on the grass which is a ***** and can make you loose .5sec just like that...
Hope it helps
PS: once again it takes TONS of practice... I talk a lot but can't do a perfect lap yet... When I drive the track correctly and COULD reach 1.41, I end up doing a tiny mistake somewhere that makes me loose time...
My Optimal is at 1.41.3 or something... though my best is pretty far at 1.42.1... This track is really vicious lol