Leak to Right Rear Floor in '87 Coupe GT

["Robert E. Calem" <"rcalem@worldnet.att.net"@postoffice.worldnet.att.net>]

I have a major leak somewhere that is leaving a big puddle, nee a minor 
lake, on the floor by my right rear passenger in my 1987 Audi Coupe GT. 
Nothing else is wet. Not the upholstery, not the side panels, not the 
roof panel. It collects during rain, and a friend thins it is a clogged 
gutter that apparently helps drain water away from the sunroof... a 
gutter that supposedly travels inside the body of the car. Does anyone 
have any idea for me to diagnose and fix this problem? Please advise 
soon. Thanks...