Pull harder. There are no fasteners on the bottom of the heater core in the 95-99 legacy. Every time I pull the heater box from one it feels like I'm going to break it.

I can jiggle it pretty good but It's hanging up on the box next to it at the top right. I know if I start prying on stuff I'll break it. 

Yep, I went caveman on it and jerked it cleanly past whatever it was hung up on, 

 

Now for the replacement exercise...I'll be back.

Windshield seal leaky.