Transformers are just wire. (and a thermal fuse) They sometimes fail, but
have a very low failure rate compared to other components.
And they don't fail gradually. They either work or they don't.

The electrolytic capacitors in the power supply may need replacing, and the trimmer
could be dirty, but the trimmer may be fine as well. Replacing perfectly good
components in the power supply (not the transformer) probably makes more sense
than in other parts of the circuit, as a failure in the supply can cause damage
to other sections. But I don't usually replace semiconductors in a supply unless
they are not working. If a regulator has been run really hot for many years, I will
replace it, even if it seems to be working.

But I don't understand why you would wait for a chip that isn't needed, since it seems
you may have found an issue with a membrane flex cable. I would think you would want
to see if what you did affects the operation of the front panel.