Driver Side Windshield Wiper
 

I have owned my Mazda 3 for 5 years (purchased February 2005). On multiple occasions over the years, I have experienced some issues with my driver side windshield wipers.

I will be driving in the rain (or snow) and suddenly, my driver side wiper will no longer give the full range of motion, though the passenger side wiper will still wipe correctly. This issue then causes them to collide. The first time this happened, they collided, bent and scratched my windshield. To correct this issue, I can pop the hood and tighten the bolt, though, it still comes loose eventually.

I have talked with the Mazda dealership mechanic and they have said that the arm is designed to loosen up rather than burn the wiper motor out if the wiper encounters resistance. However, there seem to be two potential flaws in this: (1) it ONLY happens on the driver side... I have never had an issue on the passenger side and (2) this happens when it rains as well as snows, so there would not be any resistance to speak of that would loosen the bolt.

Does anyone else encounter this issue? If so, what has your mechanic's response been? Has it been a repeat issue with your car?

It's probably the nut that holds the wiper onto the shaft - which is connected to the wiper motor. If the nut loostens up the threads from the wiper to the shaft break loose and the wiper slips - causing the right and left to fall out of sync so to speak.
It is possible that the cam attached to that shaft is slipping, which could be spot welded to fix. But if it's the wiper side just take the wiper off (you should be able to force it to twist on the shaft to get it loose). Then clean out the threads on both sides and make sure to retighten it in the correct position. If the threads bite well you'll have no more issues. If the threads aren't cleaned well, or if it can't be tightened enough to bite in - you'll need a new wiper, possibly a new pivot piece as well to get a clean connection.
The shaft is hardened by the way, so don't try and drill it - otherwise just a pin would work to hold it in place.