My question involves landlord-tenant law in the State of: California

I noticed shortly after moving into my apartment (on the second floor) that there is a large crack about 15 feet long in the concrete walkway in front of my new home. The crack is so large it caused two segments of concrete to sag, resulting in about 2 1/2 inches of standing water when it rains.

I notified the office originally 9 months ago. 30 days later, I asked for a timeline on when it would be fixed. They hadn't even properly submitted the repair request form, so I had to re-request the repair. Their idea of a fix? Put plywood sheets over it for when it rains. I explained that the water leaks out from under the walkway, which could result in structural weakness, so they cut out a section from under the walkway to inspect it. The wood is rotting, as I feared. I had a friend (who is a contractor) examine it, and they expressed extreme concern for the safety of anyone walking on it, to the point that they refuse to visit now.

I'm about to check in with the office for the fourth time on any possible, tangible repair. Should I type out a notice of withholding rent for when I do? Is it severe enough to warrant such extreme measures? That walkway is the only way into my apartment, and needs MAJOR repairs.