A good long blast of WD40 pointed down the shaft (under the headlight) will normally get it moving again. Ultimately you may need to take the unit apart as it will likely be a loose or gummed up gear wheel(they are small, made of Nylon and don't last for ever).
There is a "how to" on BillJ's website (see link at top of page).
I would recomend a 'sooner rather than later' approach to taking it apart. I had one that stuck vertically intermittently. By the time I got round to looking at it, the motor had burnt out. They can be stripped but are fiddly and full of grease. Look out for the small ceramic conductor that is very easy to break. Also the spindle can get corroded making stripping dificult.
While you have the healight out it is worth splitting it apart anyway to give it a clean out. There are a series of spring clips holding the lens onto the main part and once apart a wash with soap and warm water ( VERY CLEAN, SOFT CLOTH ) improves the light output remarkably. Rinse with fresh water and allow to drip dry. I found that the drops of moisture ran off and left no deposit.
you were able to rinse and drip dry with no deposit because you are blessed with Scottish water. Further south, we enjoy water full of calcium carbonate deposits which are left on the surface after drying.
I'm not sure what Belgian water is like (there always seems to be something more appealing to drink whenever I'm there), but I would recommend rinsing with distilled water if there's any doubt.
Now it seems the wiper works from time to time. It's stranded again in upright position. I remember reading in the forum somewhere some tips with turning on and off the ignition key ? But I can't find it anymore.
I know this one! Have a look at BillJ's site, it hasa info on how to fix the headlamp wiper problem (look under info/utilities, then electrical). Another thread to look up is my thread on this site called "Strange problem!!!???***?!$*" - it has a link to another site that mentions a mod to the diode controlling the wash wipe mechanism, if you read my thread you will see what can happen if you ignore this problem too long (like I did !!!! doh)
Hope this helps
Of course you can park them permanently by taking out the fuse (can't remember the No. right now). If you do this remember to put it back before the MOT or you'll fail for lack of horn (and no smutty jokes please) . They run off the same fuse...