It's not the Lefty (which will be a good or bad fork dependant only on one's opinion) but the wheelset/rider.

I left wheel has exactly the same stresses on it a a wheel with a conventional hub.

Assuming you are a really smooth rider, then it's the wheels. MAVIC 117s are pretty much the entry level rim, so not as sturdy as the better ones. Add a less than perfect wheel build, and you have a recipe for disaster.

You need new wheels now, so just get what you pay for (higher end MAVICs are great, RhinoLites are good too)! I don't know what wheels cost over there - but don't penny pinch, you will regret it!

Ensure you get them built properly, because even the best materials will fail if the wheel is not built well.

When you've got a good reliable wheel, ride your Lefty for a while. It won't take you too long to realise that they are as good as most of the stantion forks out there, and usually lighter. If you dont like it then, give me a PM, I could be interested.