I rent tanks on a regular basis and the O-rings are almost always bad (either that or I'm just unlucky). I almost make a habit of swapping out the O-rings just because I don't trust theirs or there is obvious wear (have had at least two blowouts, both above water). I usually have O-rings with me, but Robert even gave me a couple, heh. Fortunately, I haven't had an SPG O-ring issue yet, but it doesn't sound fun.