Parking is easy as long as your carefull. A bottle of phosphoric acid at the hydroponics store is $10 and a kilo of zinc phosphate or Manganese is under $20, a gallon of distilled water a pad of steel wool and your all set. That will do a couple of 870's. 3 oz. of acid + 3 oz of either the zinc or the manganese per gallon of water, Throw in a bisquit of steel wool. Boil for 10 minutes before adding the parts. Add the parts, back off the boil to 180 deg f. Let the parts simmer for 20 minutes, take them out rinse in water and spray with wd 40. The parts MUST be totally de greased before parking. Do not touch them with your bare hands. If it comes out of the tank and looks spotty, de grease and throw them back in for another 10 minutes, rinse and oil. It's not Voodoo or witchcraft, and if you don't like the results you can do it again. I like the Zinc phosphate better, it's a little more grey than black. To top it off give it a teflon coating. With some guns the hardest part is stripping them down to nothing (or getting them back together again)