Well it certainly didn't take long to get a positive response from Rhoades Car.
At 1614 hrs I got an e-mail from Beth at Rhoades Car. She had shown the pictures that I had sent to David Rhoades and he had told her to ship us a set of two new derailleurs at no charge, as quickly as possible.
As from the start of our experiences with Rhoades Car, I continue to be impressed with the level of support that the company gives their products. If there is a problem then it gets fixed quickly!
I will continue to provide updates on this issue here as we hopefully get our 4W2PCP back on the road soon.
As mentioned yesterday, after our ride downtown on the Colonel By Drive, I was cleaning the quadracycle and noticed that the left-rear Sun Race derailleur had a crack in it.
This morning I got up early and went to work on it before the day got too hot. I blocked up the Rhoades Car and removed the derailleur. It was an easy task and only required three metric hex wrenches. Sure enough the derailleur itself is broken right through on the upper mounting portion. It is apparently a non-steel cast part and seems to have suffered from crystallization, a typical failure mode for this sort of part.

While I had the Rhoades Car blocked up I checked the other derailleur and sure enough it was visibly cracked in the same location. So removed that one as well.

Next I called Beth at Rhoades Car. As always she was helpful, friendly and efficient. I offered to send her photos and she said she would check and see if the derailleurs are covered under warranty at this point in time since I bought it 17 months ago. We have had the quadracycle since February 2007 and have ridden about 900 km over nine actual months of use on it.
At this point I am waiting to hear back from Beth as to what we do next. Basically if it is still under warranty then Rhoades will replace it and if not I will get the parts locally.
I am just glad that this didn't happen on a ride far from home, such as on our upcoming camping trip. I always carry tools and spare parts, such as inner tubes with me but two broken derailleurs would have meant a long walk home.
I will post more news when I have it.