Help Anyone

[Mack]

So here's the deal. My detacted garage is old (like 80+ years) and still in very good condition. However it has a flat roof and the thing just started leaking. Has anyone here every done any work to fix a flat roof and could they make suggestions to fixing the roof. Options that are not available at this time. Knocking down the garage and building a new one. Adding any type of secondary roof to the existing roof (thought of but can't due because garage was built before code and is out of code because it is too close to the property line so I can't build another roof on top of the existing roof) The roof looks like a tar paper flat roof. It is not leaking bad and was just hoping to seal the whole thing. Any suggestions?