Dethleffs Globebus I 3 - Windscreen Wiper Problem

Has anyone with a Dethleffs A-class motorhome experienced windscreen wiper problems.

I have a 2008 Globebus I 3 (on a Ducato X250) which I have owned since new and periodically have experienced wiper failure.  When it first occurred at 3 years old I had the wiper motor replaced under warranty (it's a Dethleffs/Hymer part not Fiat apparently). Over the intervening years there has been the odd problem with them stopping mid-wipe!  After a while, sometimes after only a few minutes rest, they start working again.

All was well until the last trip out when they stopped working 5 miles from home and when I switched off the ignition and started up again they gave a few sweeps and stopped.  Have tried again today and they are still playing up.  My dealer has a backlog of work so can't look at it for a while yet.

Does anyone with a knowledge of electrics have any ideas please - could it be an earthing problem or perhaps a dicky ignition switch and not the wiper motor at all!!?

Oh heck it's just started raining here!!!!!!!!!!!!!!