Another waterproofing question: our basement has a walkout door that is leaking from where the metal doors meet the concrete base. Three pictures from inside and one from outside are attached below. The metal doors extend beyond the small stop at the top of the stairs, so rain is draining (correctly) to the outside perimeter. However water is able to weep inside. There was old, probably latex-based caulk on both sides of the door stop, which apparently failed.
How do I repair this? Do I have to clean out the existing caulk and start fresh? Or is it possible to clean it and add a compatible latex-based caulk?
If I have to start from scratch, what should I use? I found several suggestions for caulking concrete (similar to this question plus hydraulic cement):