This simple question might have a not so simple answer, and I want to ask it about a single lense, but assume that would be off topic, because I'd basically be asking 'should I buy this to repair my other lens?'
Here's an example: are the lens elements from the nikon 18-55mm vr ii compatible with the elements from the 18-55mm vr? They look cosmetically similar. Is there a spec sheet?
Same with other lenses, like the 50mm 1.2 ai-s and 50mm 1.2 ai. Compatible elements? Spec sheets?
My example comes with real world motivation: I got a free lens from a friend, wanted to try my hand at repair for cheap. I saw a lens with the same specs, same generation, but one model newer or older and it's af motor is damaged, or something similar.
Feel free to edit my comment if you feel it can be better phrased.