Greetings everyone. Please excuse my novice-ness, as I am quite new to the AR format. I'd like to have a supply of spare parts on hand, and I was wondering if this one, or any of the ones listed below it, are good buys. DPMS Parts dpms field repair kit, dpms ar-15 p - www.AR15Pro.com . I assume these are the most common parts that wear out or break over time? My lower happens to be a DPMS, if that matters.