1997 Heater Core Replacement / Heater Valve question

[c5t4r]

Long story short - car got hot, coolant was low. Heater core was replaced 2 1/2 years ago, so didn't check that - no other signs of leaks, no signs of head gasket problems. Topped off coolant, 3 days later coolant tank is empty....pulled the rug back and saw coolant coming out of the heater core housing.

I assume this "new" core is now bad too. I have a trusty Haynes manual and I'm mechanically inclined, it doesn't look like a terribly hard thing to change out. I've just never messed with the heating and cooling systems much.

When looking up parts I saw a heater control valve and of course the hoses - I just want to be sure that valve is located in the engine compartment, correct? Or is it something else that could be leaking inside?

Are there any other precautions/things I should look for, or it is pretty safe to assume it's the heater core? I just can't believe the first one lasted 7+ years and this one lasted a little over 2.

I want to get a new core in my hands, then when I take it apart make sure that's really the problem before putting in the new one.