Re.: Gear linkage.
I replaced my front an intermediate with a stainless steel/nylon from JMG Porsche.
Apparently, the standard linkages last iro 22k. So buying the machined alternative means that when the car is a pile of rust, the linkage will still be A1.
Okay, wiper arm con rod.
Both short and long con rods are available from VW Heritage £14 and £17 for the short and the long respectively (plus VAT).
This won't be the cure however.
Many on here will say to buy a clip.
Well, I think that's not really curing the problem.
When tackling mine, I first had to get a wiper motor/arm frame.
This thankfully had a good ball on the off side crank arm. No point buying a con rod if it's going to pop off a deteriorated ball.
After re-assembly, the new con rod popped off.
Back to the drawing board.
I found that the shims that sit on the underside of the crank arm between the arm and the frame were so worn, this was the point of friction. Once I added a couple of wafer thin shims and lubed it up, the con rod did not pop off.
[Having a power pack is so useful when fixing these Porker malarkey problems]
Things to note:
Removal of the wiper assembly is not difficult but necessary. For the price of 2 con rods, why not do both? You will not get access to remove the crank arms and con rods without taking it out.
It requires removal of the blower motor. Loads of screws on the blower cover, mounting points (10mm), some electrical connections and loosening the 2 x 22mm bolts that protrude through the aperture underneath the screen.
Please coat these protrusions liberally with de-blocker and allow to soak, especially if it's an aluminium frame type of wiper assembly. They can shear.
Also use some deblocker on the 16(?) self tapping screws into the blower motor cover. I replaced these screws with ss but 1 sheared beyond salvation.
A little bit of Wynn's gasket maker along that section mitigated it.
While you are in there...

It gives you an opportunity to check blower motor, the Vacuum pipes that operate the air intake flaps and I did some rust treatment and painting to tidy it all up.
It's not difficult, just a PITA - time consuming. Getting 2 (correct length) crank arms with good balls for the con rod attachment will be your biggest challenge.
Removal is all there in the Clark's garage notes.