There are not a lot of original parts left on these beasts. New electronics, new engines, new nearly everything that can be replaced.
I remember getting to Kadena where they were still running them out of there to bomb NV. They got moved to Guam because the locals protested them. So they swapped the KCs at Guam for the 52s. The locals never got that a KC going down loaded with fuel was just as dangerous to them.
i’ve got he original hatchet that george washington used to chop down the cherry tree ... it’s only had three new handles and two new heads
Old airframes crack. To repair them one makes a "stop drill" hole where the crack stops. Then a plate is pop-riveted around the area to restore some portion of the original strength and rigidity.
Electrical cables also break or fray from vibration through time. New cables are laid in and connected in place of the old. The original cables often cannot be removed because they are laced into nooks and crannies of the airframe.
As a result, each B52 weighs several tons more than it is supposed to weigh, and is not a rigid as is should be. They are a hazard to the safety of their crews.
If they are still considered worthy of their mission, they should be manufactured anew.