If I remember correctly these plastic ones are pinned in, if the pin is broken, your SOL. There was someone, I think in the Classic and Vintage forum, that had his local LBS get some in for 9.95 for 3. You might check there. I think Dr. Cannondale said Mikes Bike in CA might be able to special order them for you but they are getting hard to find due to the changes with the company. I lucked out. Mine are older metal ones that they riveted on.
Found it, Part # is A113
http://www.bikeforums.net/showthread...er-available..
Any adhesive is only as strong as the paint, and that usually isn't to strong on these older paint jobs.