i often get lots of oil from a friend who works in a warehouse. cases that have a leaker or broken box. i had 5 odd qts on the shelf and hadnt got into the stash to get 5 that matched. work van needed a change. i used 1 m1 15w50,1 m1 ep 15w50,1 delo400 15w40,1 mc 5w20,and 1 redline 10w30. got some weird looks over that.was told to kiss the seals bye bye. i doubt it could be that bad.this van has run a mix of m1 15w50 and 10w30 and uses a qt in 5k. how bad could it be?