Do a search on this forum. I've seen a few long threads that discuss lubricating the wiper mechanism. Be aware that there are a few versions of that wiper with different procedures for disassembly.
If it is stuggling to operate you shouldn't let it go too long as it can score bushings and shafts as well as overloading the motor.
For a lubricant, I use Dow Corning 33 extreme temperature grease (silicone based). It comes in medium or light consistency (can't remember which I used). Where I'm located it can get down to -30 C, so I don't want the grease in the wiper mechanism to go hard as a rock.