I can see that you could do a full inspection and redo all the AD's, but
for a glider that has a limit life in hours, if you don't have the number of hours on the glider, how do you show it's not over the limit?

Airworthyness seems a strange blend of physically knowing you having something safe to fly but also having the paperwork that makes it legal to fly. In this case, the first seems relatively easy, but the second is more interesting.

Aviation seems a process of learning new stuff one has not seen before. I'd like to hear how one does the second. I'd be asking

Does the plane actually have an hour limit?
What clues are available as to what time it has?
What does a mechanic you trust suggest?