Be careful if buying any used aluminum tanks. The DOT has put out warning on tanks made between 1982 and 1992.
Trouble comes from the aluminum alloy used. Only been a few cases of failure - DOT is erring on safe side and issued the notice.
I just had to scrap four tanks I've been using for 10 years - no one would hydro or fill them.
Dive shop I deal with had to scrap about 70 tanks - OUCH.
Likely others will be finding this out the hard way and perhaps try to sell the worthless tanks to unsuspecting diver.
Easy to check - look on neck of tank for original date - should be in line with brand , size , etc.