Legal Question in Real Estate Law in California

I'm cautious to give you a green light to proceed with a repair-and-deduct remedy as might otherwise be appropriate because the landlord, who apparently is not the most ethical and above-board around, may have an argument that (a) the garage is not part of the premises that are demised (rented) to you, and (b) a non-locking garage door is not one of the "dilapidations" for which a tenant is entitled to do a repair-and-deduct. Nevertheless, if I were in your situation, I think I'd get the door to lock somehow rather than risk a burglary, especially if the repair cost is low in relation to the value of your property. Then try the deduction routine and see what happens. Maybe you'll get away with it, maybe not. As to whether you have an actual right, I'm somewhat doubtful.