is Lifter sludge normal?

[Bilgewiper]

I have never taken a used lifter apart before. Do they all store this stuff up? This sludge came out of this lifter from my 98' Vortec 350. I replaced them all because one was rattling on start up if motor occassioanlly stopped with valve pressure on it. Couldn't tell which one was bad. The valley had just a slight trace of sludge. (one owner 84k. miles almost exclusivley mobile 1 oil at regular oil changes). I know this is the wrong forum to debate the use of Dexcool, but this thing has always used about 1qt. of Dexcool per 15k. miles. Wondering if a leak to the inside of the motor, say past the intake helped make the sludge? Anyway I took 4 lifters apart and they all had the same amount of sludge in them. Also couldn't compress them like the new ones I put in. Hopefully in a few days I'll have it running agian.