20-50 is thicker, meaning the ****s are bigger, so they won't slip through the cracks as easily. come to think of it, I go through about a quart a week, gotta take some time on my day off and find me own leak.
Wow! I can't even guess how many QTs low you were if it didn't even register on the dip stick. But, if it the motor wasn't burned up before, it certainly is now...