Recently purchased an old Hirondelle Manufrance 10 speed, posted pics up here, and many suggested replacing the Simplex rear derailleur~possibly with a SunTour. Happened upon a Simplex SEVEN on a Univega at the local pawn shop for $25. Should I purchase said Univega and make the switch? Or trust that the Simplex will last (barely used). As usual, thanks for helping out a newbie...