I ran into something similar, during the course of a solo II event the car would oversteer more as the event went on (which also explained the problems I had on the road course at HPR in CO)

anyway I had to drop the spring rate in the rear 50 lbs. then I switched to the soft compound Hankook's with the 225/45/15 well that took care of the front wheel spin (at least while they were fresh)

Now based on front shot pictures it looks like the car is rolling 3 degrees so I am going to go up on the spring rates on the front which might lead to me going back up on the rear spring rates

Another thing I am learning (which is speculation on my part) is one of the reasons that fast drivers are fast is how they handle the rear of the car

Let me explain, it is often said a loose car is quicker/faster but its really has to do with what you do with steering wheel

Me being a slow poke driver I tend to hold the wheel into a turn just slight bit longer before I let the wheel release
Now if the car is setup to oversteer slightly I will tend to spin the car or just have all kinds of problems

my co-driver (a friends son 25 years old but a national level RC car driver) would tend to release the wheel just a little sooner let the car track out and would hardly ever have problems with my car oversteering

Now the result of holding the car in a turn just that little bit slows the car and you end up scratching your head why am I slow I am doing everything right

Anyway a few thought and observations

Davegt74