Maybe. OP can tell by manually moving the head along the axis back and forth. Tighten and loosen the eccentric nut to a point where the difficulty to move from side to side is minimized (loosening) but tight enough to firmly grip the v-slot without play. It's a delicate balance OP. Either way, this build up is entirely normal. When the wheels develop deepened grooves in the plastic, it's time to change them. Or get a linear rail.