* The reason your washer is only washing the back window is that there is a single pump, which is bi-directional, it has two outlets, one to the back and one to the front. There is a small pellet between the two output ports, this swells and gets sticky. When the motor changes direction there should be enough back pressure to push the pellet to the other side, but once it has swollen it get stiff and, as there is more resistance because of the single jet on the rear wiper, when you try to wash the front screen, which has four jets there is less back pressure in the pump, so it cannot push the pellet to cut off the rear washer.
To fix it, which takes a bit of time but doesn’t cost anything, you need to undo the self-tapping screw holding the inner, plastic wheel arch protector (I did not need to remove the wheel). You will then see the washer bottle and motor. Disconnect the electrical plug from the motor (it just pulls off). The motor and pump can then be pulled out of the bottom of the washer bottle. Pull the two pipes off and you should be able to see the pea-sized pellet between the two outlet pipes. This part is just a press fit onto the pump and can eased off, you can then ease apart the two parts that the pellet lies between. You will see that the pellet has two tapered ends, these must not be damaged but you need to reduce the outside diameter of the raised parts – either using coarse wet and dry paper or a sharp, fine file – until it is a really loose fit in its plastic housing (on this part precision is not necessary). Then snap it all back together.
I did this several years ago and it hasn’t given trouble since. I did cover the motor in plenty of grease, as it was very rusty on the outside. What really decided me to attempt my own repair was that there was not a direct replacement available and I did not want the excessive expense of having the unit replaced as the replacement would have been a two-pumped bottle and new wiring would be required.