How to tell if hollow stringers are bad? 20' 1969

[69Seacraft20]

Well that's good news! I have no real reason to suspect anything is wrong with it...just old boat anxiety. Transom looks and sounds rock solid even with 526lbs hanging off of it but deck will need to be redone eventually. I'm not sure if I have to pull the liner out or cut to replace deck. That link "this article" did not work.

Thanks!