I traded a set of 104's for a set of steel lp (2400) 80's (plus cash), around six years ago, for use as rebreather and sidemount bottles. Both tanks were in hydro, good for three and two more more years, at the time. I had one hydro'd when it ran out...passed with no problem. Used them (and filled them myself, despite the one being out of hydro....both tanks clean visually every year) maybe a dozen times over the past four years. Decided to get the one hydro'd a couple weeks ago, ...took it to the local hydro facility...and they said they could not test it because the serial #'s were not legible.....I looked , only three #'s are discernable, it looks like they "over galvanized" the area over the serial #'s. The hydro facility even tried wire brushing away the excess "coating', to no avail.
Does anyone know if there is any recourse to get this cylinder replaced...I believe it is a Pressed Steel manufured tank? Or is the original warranty only to the original owner?
Just a shot....never seen this occur before, in over 40 years of dealing with SCUBA cylinders.

Thanks