bolt won't tighten down

[eddieshep999]

I have a Spyder RT-S SE5 2010 MODEL

I have fitted the Diamond R Accessories arm rests
To fit it you have to remove 2x6mm and 2x13mm bolts, put the armrest plate on then bolt it down with the 6mm and 13mm bolts

I have found on of my 6mm bolts - the rear one which also holds the rear Handbar cover plate will not tighten down
I belive the bolt fits into a thread sleeve in the plastic and this has become loose and just turns with the bolt
anyone know how to rectify this
Did think about drilling down where the bolt goes in and using a longer bolt adding a nut but not sure whats underneath and don't want to hit something with the drill

Anyone know how to overcome this problem

Thanks

Eddie Sheppard
Reading UK