There is a method called the salt and alcohol treatment. I think it might also be called The Doctor's Pipe Sweetening Method or something like that.
This is what you are going to need:
1) Pipe Reamer
2) Grain Alcohol or the highest proof alcohol that you can get
3) Salt or cotton balls
4) Pipe Cleaners
5) A single pipe stand or something that will hold the the bowl in an upright position
6) An eye dropper or similar tool
Here is what you do:
1) Remove the stem from your pipe
2) Ream the bowl. Remove as much cake as possible. You can leave a little cake or ream it back to the bare wood, your choice.
3) Insert the thickest pipe cleaner that will fit into the shank of the pipe and into the draft hole. That way no salt or alcohol will start coming out of the shank.
4) Fill the chamber with salt or cotton balls. (Some people don't like to use salt because they say that the salt granules could get into a small hairline crack in the cake or wood and when it gets wet it will expand and make the crack bigger. If you use large salt, like Kosher, I don't see where there will be a problem. But if you are worried about it, use cotton balls. They work almost as good.)
5) Using the pipe stand or whatever, position the bowl in a stable upright position.
6) Using an eye dropper or something like that, slowly add the alcohol onto the salt or cotton. (The reason for using an eye dropper or similar tool is so that you can control the amount of alcohol that you are adding. If you get any alcohol on the finish of the pipe, it will start stripping off and ruin the finish.)
7) Be very careful not to get any alcohol on the exterior of the pipe!
8 ) Let it stand for about 24 hours to make sure that the alcohol completely dries.
9) While the bowl is soaking, clean the stem using pipe cleaners and the alcohol.
10) After 24 hours or whenever the alcohol has dried, empty the bowl and repeat until the salt or cotton stays clean and white. Or as close to clean and white as it will get. (On a very dirty bowl, you may need to do the treatment quite a few times to get rid of the taste and smell.)
11) Do not get any alcohol on the outside of the bowl!
12) Once the chamber is clean, thoroughly remove all traces of salt or cotton from the chamber
13) Replace the stem and let the pipe completely dry by letting it rest for a few days. I recommend letting the pipe rest for about a week so that it is completely dry.
Some people use and will say to use isopropyl alcohol. I have never used anything but grain alcohol (190 proof). That is my choice and I am just explaining how I do it.
I hope this helps you get that pipe back in shape.