Reverse is at the far end of left right travel for the gear selector so any play in the shaft might mean it doesn't make it all the way over. Does the gear lever feel loose when you move it left to right. This is a normal wear part in the gear lever - there is a little half moon with a slot in it that sits on a dowel and the plastic wears. Mine has gone after 40,000 miles and it's common. Alternatively as they say look at the clutch but if this is dragging it will also be harder to get first stand-in still. In just in the process of doing mine now if it turns out to be this happy to help
