[GBA]

When was the last engine upgrade? Swap out the 8 old for four new high bypass turbofans and keep it flying for another 50 years.

[SJSAMPLE]

That was already discussed and dismissed, over a decade ago.
Still worth reviewing every ten years or so, just to see if it’s economically feasible.

[Erasmus]

When was the last engine upgrade? Swap out the 8 old for four new high bypass turbofans and keep it flying for another 50 years.

Boeing (IIRC) has a plan to do just that. Replace the eight obsolescent engines with four CFM high-bypass ones. Year after year, it falls below the cutoff line in USAF budgeting.