Have you popped the jets off the shaft, as if you were going to remove the arm, and run some wash through the system?

Also with the jets off try an air line on them, I know that when they are blocked, they are really blocked
A soak in hot water might soften things up too, after all it's mainly dried up screen wash, unless someone's been putting Fairy liquid in the system........... you have a lot of unblocking to do then  Yesterday I couldn't spell Engineer... Today I are one!
Inventor of the 'Guide-o-Matic automatic wheel alignment tool'
Former long term L322 owner, Up/Down graded to a Classic Tractor!

Didn't know you could remove the jets like that, I'll have to give it a try. Do you need to remove the spoiler to get at them? NW060

"Red Shed" - 1982 Series 3 88" County Station Wagon
"Spirit of Great Britain" - Rolls Royce Meteor V12 engine
ZG875 - Westland Sea King (cockpit section)
"Carly Rae Jeepsen" - 2006 Jeep Commander 5.7 Hemi
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"Georgina" - 2000 Discovery 2 TD5 ES - sold
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Yes you do, but that is well easy to do, if you open the tailgate and look at the dirty bit at the top there are 2 x 10 mm bolts (M6 thread) which you need to remove, then shut the tailgate and slide the spoiler towards you (away from car) and it should lift off (key hole slot in spoiler locks on to pegs in top of tailgate).

Then it should just sit on the roof and you can get at the wiper assembly

Ps, give the wiper arm a good work out with some oil, as they tend to corrode up and hold the wiper off the window  Yesterday I couldn't spell Engineer... Today I are one!
Inventor of the 'Guide-o-Matic automatic wheel alignment tool'
Former long term L322 owner, Up/Down graded to a Classic Tractor!