Itermittent wiper problem

Just recently my windscreen wipers have developed a problem.

When i switch them on at the lowest speed, they go across the windscreen and stop for about 10-15 seconds then slowly return to the bottom but not quite making it all the way down before stopping again.

They work fine on the next setting up but i am worried that it the problem will get worse, i live in NE scotland so we get alot of rain so i need my wipers to be working.

Any ideas or has anyone else experienced this?

Thanks

Could be the internal switch in the wiper. Need to remove the wper arms and heater intake to get at it. Then there are three screws which hold the gear wheel cover on. the switch contact is under this.