Headlight wipers are definitely useful in the salt/snow winter conditions over here in the Volvo back yard... High pressure washing simply cant compete, got them on my other car..
One wiper stopped working on my V70 -00, I took it out (L side: remove headlight and wiper arm, undo the screws holding the wiper motor, enlarge the hole for the shaft in the inner plastic cover and out it goes with some effort)
Disassembled it by lifting a number of plastic hooks, out fell a number of gear wheels.. Anyway, found that the motor was incredibly weak and became hot when powered, the PTC fuse actually tripped when operating. Grinded away the lugs keeping the motor back shell and found that the commutator was fouled with oil and soot. Cleaned, put it back together and glued the back shell in place. Now the real problem began, no clue how to align the gear wheels and the position switch. Spent an hour and tested most of the possible combinations using a 12V supply. Found one that seemed to work so I put it back in the car. Tested and found that the wiper tried to go DOWNWARDS. Well it couldnt since the bumper was in the way... D_mn. Took it all apart again and spent one more hour trying to find the correct gear alinment. Finally did so and put it back in the car. It works perfectly so I am not worried about fixing the other side once it goes.