I have a LOT of customers coming to me looking for replacement bolts for their AGM M4's. The stock bolts are utter CRAP, and break extremely easily.
What's worse, is that the bolt carrier is not to WA spec, so if you wanted to replace the bolt with a WA/G&P/Inokatsu/RA-Tech compatible unit, you would also have to buy the bolt carrier - in effect, you must replace it with a complete bolt assembly.
As an FYI, the complete bolt assemblies cost just a bit over $280 at the current exchange rate through my RA-Tech preorders. Taxes must also be factored in to that price, but it works out to cheaper than ordering through RA-Tech on your own. I run these orders regularly, and can get you complete internal replacements to fix up the AGM.
The RA-Tech "Magic Pin" should also be sufficient in tightening up wobble between the upper receiver and the lower.