Charlie57;
Pin hole wear is the death knell of any AR-15. It could be manufacture's tolerances, or show wear from use or changing triggers too much, but all receivers will be rendered useless when these go bad (get too big). I don't know that it is particular to just Essential Arms or cast receivers. I thought I read that there are parts and plans to drill out the holes and trigger and hammer parts that allow the accommodation of the larger Colt pins. In any event I think that DPMS will "exchange" your worn out pre-b lower for a "new" one,....for a nominal (large) fee, but only by a special arrangement (read large fee again).
lucasf;
EA receivers are Eagle Arms, The predecessor of (the new) ArmaLite. That would be a forged lower and generally commands a little higher price. My personal preference is for early Colts with Eagle/ArmaLite a close 2nd.
Kentlik;
Do the test fire and if it works get it. Don't worry too much about the day light between upper and lower if every thing else is snug.