Probably nothing. After all, a lot of guns with those old parts worked fine and some are probably still working fine with the old parts. The upgrade was done as a result of problems experienced in just a few guns.
Still, sending out upgraded parts free costs Glock money and anything that costs a company money they only do for a reason. So the fact that you could probably have gotten away with using the old parts doesn't mean that there's no reason to use the new parts.
By the way, you'd probably need to swap out ALL the upgraded parts to get back to the old configuration. Mixing some of the old parts with some of the upgrade parts could cause unpredictable results.
Last edited by JohnKSa; 05-09-2010 at 16:28..