The 123 cars and some of the other earlier models have grease fittings on all the hinge pins. On my 124 car, I use a squirt can of motor oil, work it in as best I can, and then clean the heck out of it with a rag.
BTW, the 123 pins have a fitting that requires a needle point adapter on your grease gun. I went and bought one of the miniature grease guns, and put the adapter on it permanently. I use it only for the 123 door hinge pins, and the double cardan universal joint on my old 4X4 pickup.
'84 Euro 240D, 523K miles
'88 300E 5 Speed
'81 300D Daughter's Car
Over 800,000 miles in