Its called a pintle cap.They come off all the time.Last time I needed a set I purchased them from lindertech.com.They have a huge selection of fuel line and injector parts,some that cant be purchased any where else.Give them a look.

 

im thinking about just replacing the injectors. i found some one with a set of all 8, they are the exact same ones i have in right now, for $100. i figure it wouldnt hurt to replace them all and keep these for spares.