How to keep the silver cap tightly affixed to the power On/Off lever on my Pioneer SX-1050

The power on/off lever has a silver cap  and it keeps falling off.  That’s annoying because I can’t usually see where it has fallen and have to really work at finding it.  But the bigger worry is I’m afraid I’ll lose it!  Any ideas for how to secure it?  A special glue or adhesive?