I've just remembered when I had mine fixed they get back to you when they've diagnosed the problem an then let you decide if you want to go ahead with it.
Hi you are better off replacing the entire unit not to difficult, not to expensive, but make sure you buy a new rubber grommet as that deteriorates with age and give it a liberal coating of silicone grease when refitting grommet they tend to last longer, thats probably where your leak is.
Steve.
I had the same issue so I've removed the fuse to stop it randomly wiping the window and going to buy the wiper delete kit for £10 I always wipe rear window with a squigee anyway and put the rear window heater on any way and looks good with out the wiper