OK, did as everyone suggested and installed my new blades. Seems like the problem is somewhere in the RHS (drivers side) motor or linkages.
It almost seems as it the RHS wiper either
(1) gets out of synch smomehow (if that is even possible) or
(2) has a degree of play that worsens as it warms up
This might be harder to solve than I had hoped.
My odometer stopped working last week also. It is a bugger that you have to pull the speedo apart to determine whether you need a 12 or 16 tooth gear - particularly when you have to then order it from OS and wait for the post!!
Cheers,
Peter