i have a leak on my passenger side but cant find its location or how to fix it, i think its coming from ground up so it may be a hole in the bottom but its sticky and smells bad. when cleaned up its kind of brown.
Possible rust hole through the floor pan. Get underneath it with a Mirror if you cant have it on a lift and see what you can find. If you can snap some pictures so we can help better. Inside at the location where the brown is and underneath
take a picture with your phone and head to the local pull a part and compare what is there. I have done this some when I get stumped. Sometimes the part that your missing is still intact on a car there. If its a gasket that is missing (Rubber) then you could grab that at the local parts store.
I has the same issue in a Grand Am and it was a rubber gasket that popped out of the floor pan. each time I went through the rain, the carpet got wet.