My local reputable dealer unwittingly screwed me this weekend.  He took a pre-ban olympic AR-15 on trade for another rifle and he sold it to me for a pretty decent price.  I bought it and thought I made off with a good buy until I tried to see if the thing would cycle.  That rifle had every sort of jam that one could imagine.  Double-feeds, no feeds, stovepipes, no extraction, one round jammed ON TOP of the BOLT!  I've never heard of that happening before, but it happened to me twice.  I told a friend to check the rifle out by swapping uppers to see if his upper would cure some of it's feeding problems.  He called back to tell me that his newish commando upper will not fit because the "locking block" is too big to fit inside the lower.  He also went on to say that the upper I had was ground to fit the lower.  He also noted a ground up version of a full auto bolt and other mangled parts inside of the rifle.  All in all the whole thing needs to be replaced from the ground up to be even remotely functional again...  I am NOT a happy camper right now.  I will be contacting the shop owner to see if he will refund my money or at least help me fix this POS.  [pissed][pissed][pissed]

I just went through the same thing myself with an old Oly. None of my other uppers would close on the Oly lower. It seemed like the front pivot pin hole in the lower was located too low. The Oly upper was really loose on my other lowers. I contacted Tom at Oly and he instructed me to send it (the lower) back. After about 6 weeks, I had a brand spanking new lower with the original serial numbers. And they didn't charge me a dime, even after I asked them what I owed them!!!  The new one is good to go and works great. I went ahead and replaced the trigger group with Bushy parts and bought a new Bolt carrier from Del-Ton (the original carrier was kinda banged up). It will be the basis for my upcoming M4gery project.