Heater blowing steam

Hi Guys, I have a problem with my 68 Coronet that I'm hoping someone can help me with. I recently purchased the car and its been great except for this issue with the heater.
After the car warms up steam starts coming out of the grill near the windshield and the inside vents. This continues for several minutes and then stops, for the rest of the day its all good. I don't drive the car very much and I'm assuming I have a small internal leak. I don't see any signs of water leaking or smell anything. I plan on replacing the heater with an aftermarket AC system but until then and short of pulling the heater is there something else I might try? Pulling the heater sounds pretty straight forward but having never done it I'd appreciate some feedback on what I might expect?

Usually means a heater core is leaking. You could add leak stop band-aid for a while or disconnect the heater hoses and run a by-pass.

I would bypass adding a sealer could plug something else up.

Heater core, I just fixed my 87 new Yorker this way
1. Flush core
2. Buy tube of silver seal, attach some hose to both nipples. Put a teaspoon of dealer in one tube, put other tube into a tote, run some water through
3. Buy a furnace condisit pump. Hook up one tube to outlet, other tube goes in tote. Fill with water, and run pump for a hour. Put rest of silver seal in tote

Recently, the water pump belt shredded off the new Yorker, and wife drove 15 miles home. When parked, due to pressure, the upper hose BLeW OFF!

Heater core was unaffected.

My father said " no way that's gonna work, just pull the dash"

He was wrong, I'm still driving it

Best is alumi seal also on brass works great I use it leak or no leak. Will not harm system stays in solution until a leak then cools at leak ergo no leak. Will not work on 1/4” hole lol

Is this a factory A/C car? The airbox drains could be plugged up.
Mike

I decided to do a Stealth Bypass, molded bypass hose at the water pump and tuck the heater hoses in beside the pump, have to really look to tell. Should work for now while i plan on which AC to install.

Before:

After: