I have a problem that seems to be unique, which I cannot seem to solve.

My 90 year old house, which is basically built on a slab, has a concrete "wine cellar" that projects from the rear of the first floor (ground floor), into the slope of my backyard--house is kind of built into a hill. The CEILING of the wine cellar are CONCRETE SLABS, that lie at ground level, at the bottom of my backyard hill. The slabs are cracked where they join over the wine cellar walls. This, of course has caused a lot of leakage every time it rains. A former owner tried roofing tar--of all things--to try to stop the leaking. I've tried patching compounds to various forms of cement and concrete--to no avail. How can I seal these cracks short of completely re-surfacing the slabs so I could possibly use the wine cellar space? Any help would be appreciated... Thank you. ZA.