Take around three bristles from a small wire brush and chuck them in a pin vise or razor knife holder. Trim their ends even. Place a drop of 91% isopropyl alcohol in the hole behind the offending key and gently "scritch" around in the hole with the wire brush. Be careful not to break a bristle off in the hole. This also works for HP41 keys. If possible, avoid breaking the posts. If you need to cut them, try to do it in a manner that allows for subsequent glueing or otherwise sealing them when you are finished.
