Rear screen failure happened to me a few nights ago. Parked up at work for a couple of hours, went outside to find the glass all over the pavement! Thankfully, only fifty quid on the insurance excess! The wiper arm linkage was seized solid and the Autoglass bloke couldn't even undo the 22mm nut, so he had to just fit the screen and tape it up. Phoned Renault for a price on new linkage and motor (stopped working), £65 for linkage and £180 for the motor! Plus VAT of course Sir....Bugger all on fleabay either! Being a typical tightarsed Yorkshireman, back to the workshop! Got the linkage in the vice and soaked the area around the nut in WD40 for about 6 hours. 18" long 22mm ring spanner and a lot of effort and off it came! next job was to free off the shaft. Plenty more WD and a 22mm C-spanner on the linkage underneath, with a side-to-side motion to free it slightly. Then hammer the shaft out from the top. Once out, I noticed that the shaft was steel, but the bushing it rotates in is some sort of aluminium alloy. This linkage is designed to fail!
Quick cleanup of the shaft with emery cloth, plenty of Copaslip and hey presto! It works again for the first time in years. Next up, the motor. This is designed to be a sealed unit, not to be opened. Sod that. Prise back the securing tabs between the two halves and separate. Inside is a normal DC motor (Commutator & Carbon brushes). I found that the carbon brushes had worn away almost completely. These things are VERY tiny (About 3-4mm wide and 10mm long. Another component designed to fail just outside the warranty period! Very little chance of finding replacements, so I got hold of some oversized ones and filed/ cut them to size. Re-assembled, having to cut the braids and re-solder, cleaned up the commutator with emery and re-assembled the unit. Hooked everything back together and all works perfectly! £245 in my pocket, not Renaults!
I now think the best course of action is to strip the linkage every 6 months or so and re-lubricate with plenty of copaslip just to keep things moving.