I have a bike with Shimano Nexus 3 gear, and it's stuck on lowest gear. However, if I move shift pin that changes gears it changes the gears. So Nexus itself seems to be working, but the pin is not returning to correct position when going to higher gear. Is there a spring broken that should return the pin to correct position, and if so, how should I fix it? New spring? New wheel? Lot's of WD-40?