I own an onza myself and have found the Onza tugs to be very unreliable and often snap off, much like yours!
I've now changed over to Kojak's myself and have found that they fit alot better and are a much more solid build (slightly heavier).
I'm a bit rubbish with maintaining my bike, and didn't realise at first that the Kojak's only fit one way round, so do flip 'em over and you do have to 'pop' them in for a perfect fit!
Hope this helps.
Ta