About a dozen or so years ago, I bought a used G19 from someone else through a cop buddy of mine. If I remember correctly, I paid around $350.00 and it came with 2 15rnd and 1 10rnd mag. I took it home and disassembled it for cleaning (I always clean my guns new or used before firing them for the first time). On this one, I noticed some buildup on the inside of the barrel that not even "Gun Scrubber" and my best brass brush would remove. Back then, the Glock Store in Smyrna, GA. still took walk-ins so that's where I headed. Signed in, told them my problem a within a few minutes, some blond guy (who's accent was so strong I could barely understand him) took my pistol and all 3 mags to the back. He was gone less than 20 minutes when he returned with my gun. He stated that he cleaned the barrel, replaced the recoil pin and spring.....and some other part I forget the name of, as well as the floor plates and springs in both of the 15 round mags. I disassembled it right there in front of him to inspect the barrel. If not for the wear marks on the outside, I would have sworn it was a brand new barrel because it was so clean. I asked him what he cleaned it with and he showed me a black bottle with red writing that I couldn't read. I wanted to buy some but, they didn't sell it so I was stuck with using OTC gun cleaning chemicals. So anyway..........my G19 came with fixed sights and I couldn't hit the bullseye if my life depended on it so, I went to the Smyrna Police Supply (only Glock accessory store around) and had the rear sight switched out for an adjustable one. After that, I had very little trouble pulverizing the bullseye.