my '02 bmw x5 3.0 with 150,000 miles uses 1 qt every 1500 miles. in 12000 miles the reccomended service interval I am replacing 8 qts between changes. there are no leaks. By now the valve seals are probably leaking. Believe it or not 1 qt in 1,000 miles is within the allowed tolerence for this engine. anyway, my indie mechanic says just change the filter every 6,000 miles and never change the oil. I guess he has a point but, I couldn't do that.
So lets review, 8 quarts added at oci plus 8 qts added between oci= 16 qts. or 1 qt every 750 mile of service, acknowleging that the drain is 8 qts at the end of the oci. it uses 16 qts every 12,000 miles. wierd when you look at it that way. 16x7.50= $120 that's a lot.