Roughly 1.5 years of use with PYB 10w40 and then Rotella 15w40 in my dad's 1971 240z. I have a few under valve cover pics floating around on here somewhere and it did have quite a bit of varnish, but no sludge. The can had no carbon deposits whatsoever.
I am not really sure on the mileage.. less than 1000 miles I am sure.
I am not really sure on the mileage.. less than 1000 miles I am sure.