edoh,
Before getting too involved.......... it is
probably just that the wiper arm, which is made of a soft metal , is slipping on the splines (which are a harder metal) of the shaft (spindle) which drives it.
You could try taking off the wiper arm on the drivers side and running the wipers to check that the splined shaft on that side is operating.
May just need a new wiper arm if it is, or you may be able to clean up the splines on the drive shaft (spindle) and refit the old wiper arm. I think the arm tends to bite into the drive shaft as you torque the nut, to give sufficient grip to overcome friction of the screen surface.
Don't panic captain Mainwaring !!!!
