Unlike cars, gliders are hand-made, which makes interchangeability of major components tricky. Grob might have made all sorts of soothing noises about their products & production methods (or an owner might have thought they had!), but I would be amazed if wings can be interchanged especially not singly. You mention canopies - I have a feeling they aren't interchangeable on gliders in general as well.
To be dull & nail it down, not all airframe damage would have come from a reported incident, and in the case of many of the Grob single-seat gliders, the metal frame that holds the wheel can simply reach the end of it's life even without successive heavier than ideal landings. I have no idea if the trainers have the same weakness.