Coolant coming into cab by heater box?

Hello I just bought a 90 BMY m931a2 after driving it started having coolant coming into cab on passenger side and leaking under hood. Guy said he just over filled it and that was why. Could that be true or is there an actual leak I just got it home and haven’t got to look it over fully. Wasn’t sure if that’s true if reserve is over filled if that’ll happen.
Thanks

Probably the heater core leaking. Very common to rub a hole in the core due to vibration. There are threads on replacement cores and eliminating the rubbing.

VPed said:

Probably the heater core leaking. Very common to rub a hole in the core due to vibration. There are threads on replacement cores and eliminating the rubbing.

Click to expand...

I found a few threads finally.
thanks