Key combs are what keep the keys aligned laterally.
Worn key-combs result in excessive side-to-side slop in the action.
Replacement key-combs are tricky to come by. JerryWelch used to stock NOS key-combs, but reportedly his stock is depleted. (And they were pricy -- $35/comb.)
It has been rumored that JerryWelch now offers a key-comb refelting service: send him your old combs and he'll put new felts on them (for about $5 per comb).
HalfmoonElectronics just started offering a key comb re-felting service. No reports yet on how well that works.
?SteffanDiedrichsen reports that there are two outfits in Germany who will re-felt key-combs:
If you're that sort of person, you can pull the key-combs from an M-3 (or whatever) --- if you're lucky enough to find one with good combs...
It's been reported that you can extend the life of your key-combs be gently squeezing the rivets which hold the felts with a pair of vice-grips.
Youtube user gfh110 documents a similar method in three videos
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