Evidence of leaking heater core, but unsure if it's just the core

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Heater core o-rings
3545586
20 mm iD. 23.5 mm oD

I’ll try the closest ones in my HF kit to see if they leak as an experiment , got a core project coming up.

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Adding to old thread

Plan C for Coolant on this job.

Pop off the heater pipes at the firewall and bridge them with 5/8 ID tube and clamps

Now you can drive you car while still doing the Heater core job

Push a hose against the lower firewall connection and flush about 2 liters of water to push the coolant out of the core. Now, if you spill inside, it just evaporates over time