on the fill tube. Vacuumboy23, is the fill tube inside the bag short with a spring around it, or does it come up to the top of the bag and look sort of like a Kirby fill tube?
a parts diagram for the U4127, looks like you need Style C bottom fill bags. They are everywhere, but your best bet would be to find some NOS bags. The new ones are junk, and don't filter worth a dang. Check my link, these are the bags you want.