There might be something wrong with the lines, with one jet not receiving full pressure (line blockage) and the either getting over-pressurized. Also the mounting could be a problem (but that should be obvious anyway...).

To flush the whole system do the following:

Remove the feed hose before the "T" (under the bonnet) and run the pump for 5-10 seconds. Reconnect the hose to the "T" and disconnect both outlets. Run the pump and observe if both sides give the same amount of water. Reconnect the two hoses to the "T" and disconnect them from the jets. Run the pump again and verify that equal amount of water comes from each one. Finally, remove the jets and boil them for a few minutes. The heat will remove any hard deposits. Replace everything, and verify that there is a gasket under each jet. They should be OK then.

Also, try to always use distilled water in the washer reservoir. It is far cleaner that tap or garden hose water (in terms of solid contaminants), and it does not leave calc deposits in the lines