Hey guys - Hoping to pick your collective brains about spare parts. In about a month I'm going to be attending a week long firearm training and qualification for work. I'm told to expect to shoot upwards of 2k rounds in the week, possibly more even. I'm going to be shooting an older Gen 3 Glock 21. Exact round count unknown, somewhere between 2-3k probably. So, the potential exists for my gun to be hitting the 5k lifetime round count while I'm doing my firearms week, which I know is an interval that some maintenance is sometimes recommended. I am cautiously optimistic that there will be an armorer available as needed, but I don't want to rely on that. What parts failures/maintenance should I be thinking about planning in advance for? I'd hoped to just acquire a second matching G21 to bring as a backup gun, but I'm not sure I'll be able to make that happen before my training week, and I'd hate to blow out an extractor or something and be SOL for the week. I'm certainly going to get a recoil spring to bring with me, but what else should I be thinking about? Would you guys go through Glock to get OEM parts, an alternative source for OEM parts, or be thinking about any aftermarket parts? (I do want to keep the gun as close to it's stock format as possible, not looking for any fancy replacement triggers or anything.) Thanks in advance for any thoughts anyone has!