My Covert Tanks still have oil on them the next day if I don't wipe them off, I really can't imagine those ever soaking enough up if you even put mild effort in wiping them off and cleaning.
The Blitz however will soak up some, but it's like the Storm Spec covers, it just takes time. Still, it's slow so if you wipe off after each shot and clean it after a set I don't see it being one to die either.
I have over 100 games on my one Covert Tank, and have just lightly scuffed it with a 3000 pad periodically and it acts brand new. Haven't put enough games on my Blitz to notice any performance change.