I've not had the washer jet barrels drop out from my '05 4x4 yet, but have been watching for it as my Y-reg Multipla had the same probs early on with identical-looking washer jets. The washer barrels in that were replaced under warranty -- the new ones seem to have a green ring of softer material (rubber?) in the end which has held them in firmly for five years now. For a permanent fix, search the Multipla forums, as I read somewhere about how you could put a very small screw into the 'closed' end of the washer to stop them coming out. (ie the opposite end to where you use a screwdriver to adjust them). Since its the ice that pushes them out in the cold, making sure you have a good winter screenwash mix helps too. Roll on the snow - 4x4 wants to play...!