New to the forum & new to the Glock as well. I just purchased a M17 with serial number prefix DH at a local pawn shop for $299. I have read in the forums about various upgrades that Glock as done/will do to various models of their pistols. How can I tell how old my gun is, and if any of the upgrades have been done or need to be done? Just got it this afternoon, and will shoot it tomorrow, so I can't even tell you how it functions yet! Appreciate the input!