So i have this weird leak. I know that the heater core is bad I need to replace it.

Its leaking coolant on the rear passenger floor in the cabin.

I'd really like to get this car fixed. it has no rust the subframe is good.

Any ideas where to check.

Do you park on an incline with the front up?

nope on a flat street.

If you know the heater core is bad, and you have coolant on the floor, then, replace the heater core. Any coolant inside the car is a good indication that the leak is coming from the heater core.

Its in the rear of the car why would it leak there if the heater core on the firewall

Its not on the outside of the firewall. It'* inside of your dashboard. Being in the rear floor area would only tell me its the lowest spot of the car. Fluid dynamics 101. Goto the lowest spot possible.

This happened to me and it was the heater core. Apparently, the heater core will burst a seam and leak causing this. Post back if that solves the problem.

yes I replaced the heater core and it fixed it.

Thank you for updating this.