Most of this story is illustrated in the pictures. A replacement snap ring is thicker, wider, and longer than the original part. Thicker and wider makes it much stiffer so that installation is somewhat more difficult, but that is not the show stopper. The thicker ring still fits in the groove of a good used laygear. The killer problem here is the extra length which prevents full installation of the part when the ends of the ring overlap just before it can go into the groove.

If you want to use these new snap rings you will need to grind about 4-mm off of one end to allow installation.
Moss Motors has Been notified September 30, 2013.

Addendum October 31, 2013:
Original snap ring not available. Substitute snap ring doesn't work. Sales have been suspended on the snap ring and laygear bearing kits until a suitable snap ring may be found or manufactured. Michael Pratt (Technical Support at Moss Europe) has started the process of having a proper circlip made. Samples should be in hand (in the UK) next week. This sounds like correct snap rings should be available within a few weeks.

Addendum December 12, 2013:
The circlip business has been brought to a successful conclusion. The photo shows the new circlip next to the old oversized (now scrapped) version. These have been test fitted successfully in England by Mick Pratt (Moss Europe Technical Services) who arranged for them to be made.

All is well that ends well. Kudos to Moss Motors for fixing this problem in an expedient manner.