Dewey,
While not impossible, it is rare that the BTH magnet has weakened. Or, there are certainly plenty of other things I would check first. But before leaving the magnet, with the magneto removed from the engine, does the magnetic field give a decidedly 'lumpy' feel when you spin the magneto over by hand? If it does, then the magnet is o.k.
Poor condition of the condenser, points, maladjusted points, carbon tracking of the slip ring, and the wrong point plate fitted (incorrect internal timing) will all sap current or prevent the maximum current from building up.
I've recharged magnets with a homemade magnetizer, but the proper kit uses a capacitor discharge to dump a lot of joules very suddenly into the apparatus. And that I never arranged. It has been a number of years since I have had a magneto reworked; and back then I was sending them to firms in the UK.
-Doug