I got a new tensioner block for my '06 and it is of different design;

Recessed mounting screws and no steel plate on the outside.

By the end of the first ride, it was gone and my chain was forlornly sagging.

I found an older one in a friend's parts bin and installed it.

Now the lad's '08 has the same tensioner block.

Is it headed for the same fate?

Any recurring problems with this new design.

Sounds almost like you're describing an xblox type tensioner pad which I've never heard of having problems, it is possible to snap the screws off on any the designs though

Is this the shape block you meant

http://www.splatshop.co.uk/x-blok-clubman-chain-tensioner-pad.html

Yup...that's the one.

Mine was an OEM part, though...not inexpensive and lasted one ride.

The older design with the plate on the outside seems more robust.

Weighs an extra 10 or 12 grams...but so do I ;-)

Yes, if you break it it will fall off! Otherwise fine!

As always, Cope...you're a zen master!