On older wood clarinets, tone-holes suffer from a variety of problems. Years of adjustment and overhauls (especially careless ones) can leave small nicks and gouges around the rim of the tone-holes, causing tiny leaks. It might not seem like a big deal, but multiply that by every tone-hole on the clarinet…
As the instrument ages, it dries and shrinks: as it heats and cools, it flexes. A tone-hole that was cut flat into a curved surface 50 or 80 years ago has often developed all kinds of minor warps which, when they meet a perfectly flat pad surface (if there is such a thing!) fail to contact evenly all the way around, causing yet more sealing issues.
The only way to effectively solve these problems is to re-cut the rim to its original contour.A special set of cutters is used to remove just a few thousandths of an inch of material, eliminating nicks and rendering the tone-hole flat again, allowing for the best possible seal.
Along with tone holes, keys get knocked about pretty badly and can end up with distorted pad-cups: bent to one side or the other, higher on one side than the other, misaligned with the tone hole, etc. Added to swedging and countersinking, it makes a huge difference in the final play-ability of the instrument! I often take a small anvil and make sure that each pad cup is flat before I put in the new pads....
I prefer to use Pisoni pads of tan kidskin. I also use pads of solid cork, which I bevel for each application. My personal preference is kidskin pads, with cork pad on the register key. Sometimes I add them on F#, C#, side Bb and some trill keys. Why is this? Well, cork pads have their pros and cons: they last forever, but they are noisier in operation. They make a great seal, but only on a clean flat tone-hole. On a loose (un-swedged) key, they are a positive liability. They are reflective because they are a harder material than felt, but can create an 'over-bright' sound if used exclusively. Used on the register, A and Ab, they brighten the pesky throat tones. So, if I have a stuffy C# or a side Bb that doesn't speak as clearly as its LH equivalent, I use a cork pad as part of the voicing process. Who wants a dull note in the middle of a sparkling passage? Not you!
Uneven springing is a bit like walking around in only one shoe: it slows you down and affects your balance! By increasing or decreasing tension on individual springs, it is possible to make the instrument feel more 'even' overall and, hence, easier to play quickly and smoothly. Aside from evenness, it is possible to give the whole instrument a 'heavier' or 'lighter' feel, as the player prefers. Flabby and slow, or stiff and heavy, both come between you and the music!
A nice final touch - I use a gold furniture crayon to fill the original logo and wipe hard to leave a sharp look..