Mysterious Leak in Basement

[bluedesert1001]

I just bought a townhouse in Philadelphia and was in the process of fixing it up. I noticed no problem with any plumbing at all, the walls and ceiling had no signs of recent water leakage. The weird thing just happened 2 weeks ago when there was a lingering thunderstorm with strong wind blowing from all the crazy directions. Naturally I did a walk thru around the house to see if there was indications of any leak in the ceilings. Of all the places in the house, the only place where there is a minor leak is in the basement, directly underneth a partition wall where the drainage run from the second floor bathroom downwards. So I investigated the plumbing since the drain and water lines go thru there, well luckily everything was dry; that did not surprise me because before the rain started there was absolutely no leak at all. So my suspicion natually falls on the fault of the roof. I had one roofer who maintained the subject flat roof 4 years ago to check it and he claimed that I needed a new roof with no particular explaination on my weird leak. Since the leak happend near the fire wall between my unit to the ajacent townhouse, I asked a second roofer to inspect the cojoining section of the roof to see if there was crack on the wall that may slowly direct rainfall into my basement. He told me I don't even need a new roof and there was no indication of crack on the cojoining wall. I am lost, guess I won't touch anything until the leak starts again. Since the rainstorm there has been no more leaking. My guess is there may be some small crack on the side of the drop in the brick wall between my house and the next that normally isn't exposed to water unless strong wind blows rain onto it. Any thoughts on my situation ?

[E. Dodge]

Well, I think you're all set to recieve a flood of guesses...but keep in mind more info, and even pictures might be needed to figure out what's going on. Since you mentioned the leak seems to be showing up at the general location oif the firewall which seperates your unit from another, I'd look at the roof terminations there , such as any counterflashings, cap flashings, wall corners, etc.... then look at any adjacent protrustions like pipes, skylights {if any}, and the seams of whatever roof material's been used.
Any roofer looking at your roof should be able and willing to provide you with and detailed explanation as to why you need a new roof, regardless of whether they're competent in locating current leaks.