B-57F:
Stress cracks began appearing in the wing spars and ribs of the RB-57Fs after a few years of service. Some were sent to General Dynamics for repairs. Due to the excessive cost of repairing all the aircraft, nine were placed in storage at Davis-Monthan AFB in 1972. The 58th WRS, the last squadron in the Air Force to use the WB-57F, was deactivated on July 1, 1974 after placing its planes in storage at Davis-Monthan.
Three ex-USAF WB-57Fs were used by NASA in support of various research programs. As early as September of 1968, NASA had contracted with the Air Force to operate a RB-57F for them in conjunction with their Earth Resources Technology Satellite (ERTS) program. The loaned aircraft was 63-13501. NASA installed a data-gathering sensor pallet underneath the central fuselage which carried cameras and electronic sensors. In 1972, the Air Force transferred the aircraft to NASA, where it became NASA 925. 925 was retired by NASA in 1982 and sent to storage at Davis Monthan AFB. It is now on display at the Pima Air Museum. In 1972, 63-13503 was transferred to NASA and became NASA 926. It was used as an Earth Remote Sensing Platform for calibration of satellite data. It was moved to El Paso in 1991. 63-13298 was transferred to NASA in 1974 and renumbered NASA 928. It operates as an air sampler for the Department of Energy.
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Hmm, even with their limited remaining fatigue life they seem to last NASA 9-10 years each. At that rate this one should run out this year. Assuming the other 5 as similar, they could keep one flying till the 2050s. Even longer than the Buffs.....