I've had a few come loose - I carry a box of matches in the car. Stick the match in the hole, snip off the head and it does the trick.

"Y mae dafad ddu ym mhob praidd"
1972 4/4, 1981 MGBGT, 1984 FLHT1340, 1980 XLH1000, 1990 ZX10