I have a 1979 300D and today it was raining so I get halfway to work w/ the wipers working fine until the driver's side wiper arm just lags down to wiping half the window and then to not moving at all, the Driver's side arm is messed up as it won't wipe at a steady rate like the other one, what is the cause of this and how do I fix it? I need to get this handled ASAP because it has been raining lately. Sometimes the driver's arm will wipe normal for a little bit, but then die down to not moving at all as the passenger wiper works fine. I hope there is an easy way to fix this problem. Thanks