Two weekends ago I finally did the big window guide job! (That is, dismantle the doors, remove the windows and re-epoxy the guides to them, clean and lube everything, reinstall and adjust the windows, make and attach new plastic moisture barriers, etc.)
During the cleaning phase I specifically looked for these water drains, to make sure that they were not blocked. My memory is that they were 2 small slits on the outside edge of the door bottom (door floor), tucked up against the outer door skin, near the middle of the door. They were hard to see even from inside without a flashlight shining up from below.
-David Pease
'66 French 230SL