It's a common e30 318/m3 engine problem. Just add an extra half quart of oil. Running at 4k RPM for that long time would simulate a track enviornment. Almost all e30 318/m3 owners I've met at BeaveRun run an extra half a quart or more on the track due to this problem.
I would also change the oil filter to something you know is good.
e30 M3's have a huge problem with oil starvation... even when running an extra quart. I know you track the car sometimes... look into modifying the current oil pan to stop oil starvation.