Front wipers stops in the middle of windscreen

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Hi There,
As topic says I got problem with front wipers which stops at different angles. Sometimes they are stops at fully opened position, sometimes half open and rarely they finish their cycle on the bottom as they should. When they are set on position 1 they keep working for some time even there is no rain etc.

I have heard that could be a problem with fuse. Which fuse is responsible for this? Is there anything else I can do? To be perfectly honest I am a bit disappointed by quality of Merc. I got just over three years old A-class and I already had problems with 3 door locks, water in the boot, handle and rest of cosmetic problems which shouldn't happen in that class. I am hoping to buy A, B class replacement in near future (rumoured BLK, GLA class) but with all this I might look in direction of BMW or Audi.
Anyway I will be appreciated for any guidance on it.
Thanks