Mamiya M645 Pro: How to Test Used Lenses

I recently purchased a Mamiya Pro TL body and also a couple of standard 80mm lens. One lens is not very pretty and has some dust inside, but otherwise seem to work fine. The other one is in very nice condition except for a short hairline fracture on an inner element on the outer edge (probably from a drop since the filter threads are bend). First question is which lens should I keep and second is there a way to test the impact of either imperfection, i.e. dust or fracture, on photo quality? Thank you for your help!

The lens with the cracked inner element is trash.

If the inner lens element is cracked, one has to wonder what may have caused that defect.... I don't know how minor the crack is, but that's not a usual mode of damage. Dust, on the other hand, does not affect anything unless it's severe.

Try taking images that include a strong light in the frame. Then look for halos, reflections, and reduction in contrast.

I'm very particular about lenses, if it were mine, I'd would likely not keep either.... but that's just me.