73 Dodge Dart Swinger?

i own a 71 dart gt that does that in a hard rain,its probably coming from around the bottom of the wind shield, a good way to tell this is see if the bottom corner of the wind shield looks white looking or fogged up,either that or the heater box will cause that too happen,evan a leaking heater core will do it also,if that isn't it let me know and i,ll help you find it,good luck to you,and have a good and safe x-mas.

their famous for leaking around the windshield wiper shaft seals & eventually rotting the floor out so change them.

also check to make sure your cowl drain hose is not stopped up.

Are you sure it's not leaking around the windshield? A tiny rust hole can drive you insane because it's hard to find. It sounds like you need to find an auto-body shop with some old guys (in their late 50's) working there.

Most likely it's your heater core. If you find differently, go to a windshield replacemant shop and describe the problem to them. they will give you some ideas.

similar to my ford maverick. if it's passanger side only, possibly just your heater core. both sides then its the cowl. mine was leaking under the hood, water running in between fender and firewall. to get to the cowl remove your fenders and you should see right into the side. to fix mine I ran weather strip in between metal of fender and firewall.

i know the car your talking about. i had a 69 dodge dart that did the same thing and i could,nt get into it either to fix it.

Have a body shop look at it

It,s your heater core....Or the windsheild wiper seals....