If all you need is a bumper your axle, trans, etc., are all ok.
Any other issues with your vehicle are prior. I see this so much I want to scream (no offense). People are driving 10 year old cars that are daily commuters down Barb Wire Blvd, Albatross Droppings Ave and Grocery Cart Collision Ct and after we turn their turd into a museum piece they in turn try to milk it and have someone pay for normal wear and tear. Ok, I'm done ranting.
What I believe happens is people have grown accustomed to the vehicle and do not notice all the problems. Then after something happens they then pay close attention to the vehicle and notice all the grunts and groans. You are on the right track, most likely all the grunts and groans of the vehicle have been there for some time.