WESTERLY has a hollow keel, partially filled with some sort of foam. Water got in some years ago through a leaking skeg bolt. When it was discovered, the boat was on the hard and the easiest way to drain the keel was to drill a 1-1/2" hole inside the boat under the shaft about 2' forward of the shaft seal, and two holes in the bottom of the keel (water also drained from the skeg bolt hole).
The boat was up for several months and the keel was able to dry out. Glassed the keel holes, and placed a well bedded deck fill fitting in the bilge hole. Re-bedded the skeg bolt, and haven't had an issue for 12 years. When up for annual underwater maintenance, I open up the fill to check for water (I can see right to the bottom of the keel).
Sounds like you have the dark stinky stuff, so you'll need to get aggressive about cleaning/draining it out as best you can. But you need to find out what's in the keel first and whether just making holes and letting it drain is a good solution.