Mine fell off two years ago. The end of the grip where the cap attached was damaged too, so I ordered both the grip and cap. When they arrived I found that the grip came with its own cap attached, so I ended up with a spare cap.
As was stated, replacement of the grip is a PITA because you need to get some slack in the carb cables, and the only way I could see to do that was at the carb bank end. So I postponed replacing the grip/cap until I have the tank off for something else.
You can get the needed throttle cable slack by loosening the handlebars and carefully sliding them to the left. Protect the tank when loosening the bars.
