That does suck, though I'm not one for having manga collections, paperback or digital.
And with GTO, I think getting into the vibe of what it is trying to convey, with Onizuka and its world, is more important than having a complete plot.
Like, the original opening to the anime is a banger to this day:
You see him walk nonchalantly from that bathroom, fully naked and with the don't-come-near-me-punk attitude, and you immediately know who he is.