Intermittent Wipers 1985 190E 2.3

The windshield wiper is occasionally in-op on my 1987 190E 2.3. I have experienced the following. After being on for say 20 minutes in varying positions from mist, low, high the wiper will quit normally in mist mode. Another variant is when turning to the 1st position (i.e. mist) the wiper will not work then turn to position two or three the wiper come on and if I move back to position one (mist) they may or may not continue to operate. When they do stop in the middle of the windshield, I can get out of the car and put pressure in the proper direction and the wipers will resume. Could it be the single wiper mechanism is dry and needs to be cleaned and lubed causing a overload issue, or is it something else like a relay, fuse or motor? Any help with this annoying intermittent problem would be greatly appreciated.