If you are having flow problems to the rear wash try this - It worked for me.
Remove the trim from the tailgate (6 Phillips head screws and pull clips).
Remove the wiper arm -13mm nut under the cover
Put an old towel over the tailgate latch area
Remove the hose from the gearbox lid and flush the line by triggering the wash motor
Remover the cover from the wiper gearbox (5 T10 screws)
Now you will see water contaminated grease and general gunge
The wiper shaft can be withdrawn without the nylon cog.
De-grease everything. The angled water inlet slides off the gearbox lid.
There is a seal inside that part - remove and clean carefully.
You will then need to clean up the ends of the shaft - I used 180 then 240 wet-and-dry paper. It won't come up new but get it as smooth as possible.
Unblock the tube through the wiper arm spindle and the jet on the wiper head. The jet is a push fit into the wiper arm.
You will now need 3 'O' rings - Wurth part #0468-005-20 (or same) and silicone grease used in swimming pool valves.
Grease up the 'O' rings. One goes in the recess in the top of the seal from the water inlet molding. Grease up the cogs and wiper shaft as required.
Fit the other two 'O' rings the the end the the wiper shaft and refit the cover which is now slightly compressing the 'O' rings.
Refit the hose and test for leaks in use. It should be fine.
Refit the wiper arm and retest. If it still leaks you need a new unit - $200.
Hope this works for you.

 

Some good info. Thank you for sharing.

 

I did not make it clear that the silicone grease and the mineral grease for the cogs must be kept separate.
Grease up the 'O' rings and seals and lightly grease the shaft.
3 'O' rings is the required total number and can be positioned with 2-1 or 1-2 configuration, but 3 all at one end will not reform the seal.

 

You have a Clubman so you had to do it twice . Or was this on another MINI ? Any pics.