first of all why is the water getting in at the first place? you mentioned it is in the top corner, is the windscreen seal damaged. also from previous experience try looking at your radio aerial as water is prone to leak there and sun roof if fitted. a simple test to carryout is for you to sit in the car and get someone to use a pressure washer and blast the windscreen and roof with water. this should give you an exact position for the leak. as for sealant, they are messy and are just a temporary measure. good luck
shaffick
December 2008