The doors should shut easily on the w123 chassis Mercedes, If they don't see if your door striker is missing this rubber piece. If it is you can find them here:
https://www.atpartsmotor.com/index.php?lay=show&ac=cat_show_pro_detail&pid=155479
or here:
https://www.atomicmall.com/view.php?id=Locking-Eye-Repair-Kits-Mercedes-Benz-W-CE-TD_1144115