does anyone have a bergonzoni 1/5th beetle?

well i do. and i was wondering if anyone has encounter the problem with the alloy wheel hex which is grub screwed to the drive shaft coming through the rear wheel hub carrier.?
it seems very under designed to transmit all that power through to the wheels with a single 3 mm grub screw and a flat on the shaft..
so if anyway knows of a fix for this problem can you please let me know cheers.