If its like mine then the problem is the grub-screw holding the arm to the spindle. Its got a pointed end rather than a flat and after a while the arm starts to flop about on the spindle, grind it flat and tighten it right up.....then do it again a month later...
Other than that, no there is no adjustment that I know of. The old lock nut on to a splined spindle from older models was better engineering IMHO.