Sorry I haven't been posting here lately...
Just some updates...
Nice clean summary thread:
http://www.airsoftcanada.com/showthread.php?t=102339
The clear lower M4's that are selling like hotcakes look and check out exactly like a full metal M4....except for the clear polycarbonate lower receiver. Swapping on a metal receiver is simple and easy.
I've seen enough similar issues to make a general comment on the durability of the SCARS. It seems like the flange of piston body (the black tube that is clipped onto the bolt with a big e-clip) is too weak...seems to be some kind of mild metal. After a given amount of normal use/wear/etc...the flange will open up. So much so that the piston body will "flop" around, leading to nozzle alignment issues and or complete separation. The flange can be "hammered" (really just tapped) back into place to tighten it up, but I don't suspect that that fix will last long.
I understand that RA Tech makes a steel piston body...worth taking a good hard look at.