I'd take em apart and give em a good cleaning and lubricate the stick before anything else.
For cleaning, you want to disassemble the stick as much as possible and get any old grease, soda, nastyness off the shaft. People have used electrical contact cleaner, carb cleaner, and brake fluid to clean with good results, though i would try some degreaser and water beforehand. Also, be careful if you use carb cleaner or brake fluid, as they're both pretty nasty, and brake fluid can dissolve plastic.
For lubrication, lizardlick.com sells joystick grease (molycoat), but others have noted that spray silicone works as well, and is much cheaper than the molycoat.
Provided no parts are broken or overly worn, you should be able to get a smooth feel relatively easy.
If the problem you're having is that certain directions aren't working when you press them, I'd look at your microswitches. Since you've hooked up your xarcade and it worked ok, I'm assuming the wiring is ok.
To check microswitches :
- Remove the wiring from the microswitch.
- Take a multimeter and set it on either ohms or diode checker (diode checker is easier since it usually beeps or lights up).
- Put one lead of the multimeter on NO (Normally open)
- Put the other lead of the multimeter on COM (common). At this point your reading should be 0 (or open leads). If you're using the diode checker function, it should not beep at all at this point. If you get a beep or a reading of more than zero, check to make sure you're on NO and COM. If you are, then your microswitch is bad. Replace it.
- Next, while still holding the multimeter leads to NO and COM, press the plunger (usually red) at the top of the microswitch, either by hand or with the joystick or button. When you depresse the plunger, your reading should go to .2 or .3 ohms (more than zero) or it should beep. A 0 (open leads) or beep and you've got a bad microswitch. Replace it.
- The above is for a normally open wired switch. Some games use a normally closed connection, in which case you should be using the NC lead on the button. Since it's normally closed, while you're not pressing the button, you should get a reading of .2 or .3 ohms, and when you are, you should get 0 (open leads).
If you need to order new joysticks, lizardlick carries wico sticks. These are 19.99 a piece. Not sure if they're the same model as whats in your game though.
http://www.lizardlick.com/Wico_c_150.htmlEDIT: got it backwards