FWIW, I have kept the wipers on our 300E and C220 working fine with a little white lithium grease on the shaft every time the oil is changed.
Stop the wiper in mid-windshield position by turning the ignition off so the shaft is extended. Wipe the shaft off and apply a light coat of grease.
The cars only have a combined total of 270K on them, so I guess it's a little early to tell if this works or not <grin>.
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe