The basics of a good woodwind repair are the same for all instruments. First, any side or excess motion in the key mechanism has to be corrected. Keys should only go up and down, period. If a key moves side to side, sometimes it will line up correctly and seal, other times it won’t. Also, excess key motion can be noisy!
Bassoons require a thin leather pad. Most brands of bassoon pads use a cardboard backing to hold the pad together. Unfortunately the cardboard makes the pad stiff, and that can make it difficult to make very fine adjustments on the larger size pads. To make the pad more flexible I make “cross cuts” in the cardboard from side to side. That makes it possible to make the pad “bend” over a curved or uneven surface.
One of the most important points when installing a pad is to use LOTS of glue. If a thin layer of adhesive is used to install a pad, the only way to adjust it is to bend the metal cup. A better way to adjust the pad is to heat the glue and float the pad into position, and that requires a sufficient layer of glue between the pad and the cup.
There are a variety of materials that can be used to quiet the key mechanism, adjust the pad height, and create a bridge between keys that work together. Cork is the most common, and that’s good to use in a place where you may need to do fine adjustments to the pad height. On larger keys cork can be noisy, so where practical I prefer to use a good quality felt (the felt used for making hats is perfect!). Felt doesn’t compress easily, so the adjustment will last a long time. For some keys or points of adjustment I prefer to use synthetic cork or tubing.
Finally, the instrument is play tested. Sometimes it’s necessary to adjust the pad height for intonation, other times it’s necessary to make adjustments to make the keys “feel” right. It’s especially important for the larger keys on the long joint (low D down to low Bb) to line up evenly.