Hey man,
Given that before I'd use this (place an explosive cylinder with a potential flaw next to my face ) I'd want to send it away for a hydro test and inspection.
Lips do them at £34.99 plus postage (£10, estimate) I believe. So if you knock this off the cost of a second hand bottle £80-90, you're looking at around £45 net value.
Now I could end up with a great bottle, but then again I could be told its not safe to use. With this considered its quite a punt.
I'm tempted to make you an offer but it would be lower than what you're asking. Just thought I'd present my rationale first.