Scott,
It sounds as though you may have a short in the starter brush wires, The wires will fray from vibration and then short out against the starter housing and completely drain even the best of batteries.
Rotax service bulletin 2005-30 recommends filling in the terminal area where the wires are soldered to the positive pole with silicon to stabilize the brushes and reduce the fraying of the brushes. DO NOT use an acetate containing silicon because this could lead to rust at the terminal.
This repair and preventive maintenance of the brushes should also work on the Parilla Leopard starter as they are the same part used by Rotax.