2000 Mitsubishi Eclipse Water leaking onto passenger side f

I have a Mitsubishi Eclipse GS 2000 car - last few months, every time it rains, water leaks in and floods the floor on the passenger side - I took the car to a body shop guy, who hosed the car and confirmed that the leak comes from behind the glovebox on the passenger side - took the car to a mechanic who removed the glovebox, but could not find any leaks on the firewall there - but he said the water seems to be coming from the left of the glovebox - how do I find it and fix it? The water has already messed up my audio system amplifier - the dealer tells me that diagnosis would cost $600 to remove the entire dashboard and anything further will cost more - is there a way I can fix it myself? Thanks in advance