Did it come loose from normal use or from disassembly/assembly? Exploded digram makes it appear that there is no mechanical attachment.
@Jayne , maybe the tube you have needs to be kneaded as what is in the vid @Button Pusher posted is definitely black.
Did the front fall off again or did it hold?
Ever notice how aftermarket parts for any keltec are 10x the manufacturing quality of OEM? Ruins the feel of the weapons.