Paul,
I thought this fix was just to get you through the inspection, you mean you're actually going to use the wipers, haven't you heard Pantera's melt in the rain.
Yes I forgot depending on year depends whether the wipers are right or left park. I always thought the right park was introduced with the L models, but I just checked and notice my two Pantera's are opposite (this shows how much I take notice as I don't have wipers on either, just Rainex and my right foot to get the rain to bead over the top
)
The '74L is left park, the later GT5 right park (as all later cars I've sen), but I've seen earlier Pre-L cars that were left park too.
Did DT switch back again with the later Embo bodied cars?
In theory the right park that you have with the correct angle arm should clear a better field of vision as the sweep terminates parallel to the left extreme of the windshield, rather than an arc to your left side that occurs with the reverse sweep.
The wiper motor uses a three way set of brushes for the two speeds so it sounds like one brush (or wiring/connector) is bad. Taking the motor off and bench testing it is fairly easy after removing the panel under the Passenger front wheel wheel. The flexible drive shaft will come out with the motor, unless your can remove the gear cover to release it.
Again you can source replacement parts from the usual BL sources. It is referred to as a 14W style motor. The motors are pretty easily rebuildable, especially as it sounds like your park switch is okay. Here's a link to a good UK site that carries all the parts and has a decent schematic of the motor, maybe you can print it out and take it to a local supplier to show what you need.
Stafford vehicle ComponentsGood luck