Oil weight on Porsche 944 1988?

I bought my 1988 944 Turbo and it was using a lot of oil--about 1 liter per 500 miles. I changed the oil and put in a recommended Valvoline race oil (VR1) 20w50. It almost completely stopped using excessive oil--only about 1 liter every 1000 miles or more. This is factory spec (1-1.5 liters every 1000 miles is normal usage).

Apparently, these older motors love the heavier stuff. And the race oil has this chemical that's good for the seals (not sold in "off-the-shelf" reg oil).

I'm guessing the previous owner was running some modern, light oil like 5w30 synthetic.

Good luck, Dan