Sounds like the left wiper motor froze. The wiper arm is held to the shaft with a single 8mm nut I think. To access the nut just pull the wiper away from the headlight. The motor is mounted with two 8 or 10mm bolts below the light bucket and only one electrical connection to break (4 pin, might be attached to the side of the light bucket or just laying in the fenderwell). You can see the motor and mounting laying under the bumper.
Easy enough to pull the motor and try to free up the movement, but I think you'll be in for a replacement. On the 560 I had just the opposite, the wiper wouldn't move, but I could flop it side to side as the drive shaft was shoved right out the back of the motor.
Hope this helps Larry.
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72
'02 CLK320 Cabriolet - wifey's mid-life crisis
2012 VW Jetta Sportwagon TDI...at least its a diesel
Non illegitemae carborundum.