IIRC the C-141 did end up having wing issues later in life, (and not the fuel overpressurization on the one aircraft above) and many had to have the center wing box replaced in the 1990’s, a rather big task as the box was never designed for replacement.

http://www.informs-sim.org/wsc92papers/1992_0151.pdf

http://www.c141heaven.info/dotcom/61/pic_61_2778.php
which states: “In the early 90’s it had its center wing box replaced due to cracking (as most of the C-141s did) and also underwent conversion from a B to a C model”

So it does look like the the C-141 had wing issues, not early like the C-5, but later on. And yes they were worn out.

Back on topic I think the 141 would have been a good choice for a multi-purpose cargo/refueler, even though the US airforce was not inclined to put much emphasis on probe and drouge pods, I think it would have been a great force multiplier or a good choice for other air forces that could not afford both large tankers and large lift. Perhaps a more compromised design than an airliner inspired tanker, as it is less efficient, but would have been quite versitile. I also think it a shame that the RAF specifically had the refueling capability of the A-400 deleted- sure the Airtanker group lawyers were all over that.