How long have you been driving? I think a 1:35 is pretty respectable for that car on street tires. Those things are pretty heavy.
Turn 1 is the one corner where you're not carrying nearly as much speed as you could. But make your increases there incrementally. It's a lousy corner to go off of.
Your speedo is probably optimistic, being German. But your speed through 2 looks fine to me.
Your line through 4 only makes sense if you're racing and you're protecting the corner. Especially with that car, don't turn right so early, use the full width of the track, make the arc at the top as wide as you can, always hit the apex by the corner worker, and make your time on the downhill.
Your line is fine through 5, which is important. You could carry more speed through 8, but that takes time to build up your comfort level with turning on a bumpy track at those kinds of speeds.
After you slow down after 8, you're turning in too early for 9 and (again) you're not using the whole track at a point where you really should. That said, you're getting through 9 at a good clip.
What do other 135s do at Willow? I've driven one there, but I don't remember much about it.
Here's more advice, if you've got the time and can put up with my voice.