Bruce, I appreciate your request to speak specifically, so I'll give a trivial example. The adjustable brass feet on Kundo torsion clocks came with dark brown rubber protective pads that snapped on over machined features like little knobs on the bottom. Over the years, those pads turn hard and crumble. New original pads, identical right down to the rubber material that turns hard and crumbles, are not available. So the options are to leave an otherwise nice clock with broken, missing or mismatched pads, leave off the pads altogether or make new pads of modern material. Protective feet made of clear polymer with adhesive backing are available at the hardware store, and although they are slightly larger, they are close in size. I've built a little jig that allows me to punch a hole right in the middle of them that will clear the machined "knobs" on the feet so that they are centered when installed and the result looks nice. Of course I'm talking about clocks that have little monetary value, unlike many of the clocks discussed in these forums, but that is immaterial. I strive in all cases to keep as much of the originality as I can in any clock I work on but sometimes it is not possible. Do I feel bad that I put clear vinyl feet on these clocks instead of leaving them with crummy broken or missing rubber feet? No.
Let's take it one step further - a broken part for which a correct replacement is not possible. Do we let the clock remain silent because "original" parts are not available or do we make a new part? Of course we make a new part. Is that new part a "modification"? I work in aerospace and in my world that is called a modification.
From my avatar, it is apparent that I work on cuckoo clocks, and I focus on Schatz 8-day clocks, which have marvelously-designed and -built movements. The cases are of good quality and materials, but because they were built shortly after the end of WWII, they were built hurriedly to help the makers dig out of the economic devastation of the war, so instead of taking the time to put good finishes on the cases, the Schatz people just coated them with some kind of brown paint that no doubt looked bad when it was new, and did not wear well over the ensuing years. I remove that finish with steel wool, exposing the original wood underneath that is actually very pretty - rich in color and grain. Do I then just recoat it with brown gunk to keep it original? No. I stain it and give it a light oil finish, as I am sure its makers would have preferred to do, were they not fighting for economic survival. This brings out the soul and beauty of the wood, and the finished clock looks proud.
One last point. These clocks we know and love were not made by gods - they were made by mortals just like us. And they were made against a set of limitations in time, money, material availability, as well as in engineering and fabrication experience. I always ask myself when working on a clock, "Why was this done the way it was?" Sometimes I never figure it out, but occasionally (rarely) my decades of engineering experience lead me to the conclusion it was just a bad design. If a small tweak down inside the clock, known only to me, makes that clock run longer or more reliably than it would than in its "as-built" state, I'll do it.
Sorry to run on so long on a topic that has already been well-discussed, but working on clocks allows one much time for meditation and introspection, and i think about this subject a lot.
