So, I found two abandoned scuba tanks today. They are both AL80s, both have 10 years since last hydro, and both had their valves OPEN when I found them. Externally they seem to be in okay shape. I figured I could get them hydroed and VIP'd and have myself some cheap tanks, but finding them with the valves open has me a bit worried. Does this make it likely they are rusted inside? If so, would a tumbling put it right? And what will all this cost me?