I have just had the rear screen replaced on my mk4 Espace. The Autoglass technician removed the wiper motor and arm complete prior to fitting the screen stating that it is virtually impossible to remove the arm without breaking it.
He was correct after 2.5 hour of gentle persuasion and loads of releasing agent I ended up breaking the arm. The arms internally moulded metal collar had corroded to the splined shaft and even using a puller it would not budge, use of a hammer and a vice eventually facilitated removal of collar.
Replacement arm sourced for £35.00 including vat from local Renault dealer.