methanol

my car has remove the top part of the rooft and replace a new 1 cause of the sunrooft,
so the problem now is, when encounter big rain, the water will leak in slowly and i mean very little and slow from the rooft which is not the sunrooft area but the front part of the rooft contact to our windscreen. and what am i thinking is, the car might be welded not good enough? or the rubber is torn out? any1 encounter this problem before? sifus help please.... i appreciate..... thx