99 Indy 500 Using Too Much Oil

My dad has a 99 Indy 500 air cooled. It is using 3-4 times the oil it should be using. I gauged it by marking the oil level at full with a sharpy and with the fuel tank full I ran it down close to empty. Measured both gas and oil it took to refill to measured points. Instead of an appr 50/1 ratio I used four times that amount. What has to be repaired?

99 Indy 500 Using Too Much Oil