Nothing too amazing about it. The Buff was DESIGNED for modular upgrade and replacement of subsystems from day one.
And I know of at least one family that has had 4 generations fly the B-52, in its' various models. . .when **I** flew 'em (1984-1989) we had several 3-generation B-52 families. . .
When hubby flew at Loring AFB 20+ years ago, it seemed like he had some kind of in-flight emergency every other time he flew. The practice missions were long then (12-14 hours), but were made even longer when there was a mechanical/electrical problem during flight and the crew had to spend extra hours filling out the post-flight paperwork.
Well, as long as the Buffs hang in there, that's fine with me. They're a 10 on the "Scare the cr@p out of the enemy" richter scale.