I have only used the ones without the couples, but did manage to get the same result from standard side gears.

My guess is that the actual hemishere was worn allowing the side gear (or replacement) to twist slightly and allow misalignment.  Check this for wear.

I only found mine when doing an oil change and bits dropped into the bucket.  Mine was still driving like normal with the exception of more frequent clicking while driving straight.

Well gentlemen, there has been an interesting development. The vendor I bought the lockers off has sent me replacement units at no cost.  
They have been covered under warranty. I am VERY pleased with the service, it would have been easy to simply say "Sorry" and forget about me over here in New Zealand. I mean it is not like I am going to get on the next flight to the US |removethispart|@ $1800 return.
OUTSTANDING SERVICE in my book. A true dedication to customer satisfaction. WOW!!!

Wow    When I bought mine here in Australia I was told that the warranty would be void if I ran tyres larger then 31"s.  What size tyres do you have Zeus?

33" Goodyear Wranglers. I ran 33's with my soft locker for 3-4 years and had no problems. I have dealt with this vendor exclusively for a few years now and it is for this very reason - they are awesome!!! .