HVAC system 30years old. Should I ask seller to replace?

[Jonathan Perez]

The duplex I have under contract has a few minor things to repair. One of the things I'm most concerned with is the HVAC system. The exterior unit and the furnace was manufactured in 1987 (which is when the house was built. The inspection called for a few repairs but didn't recommend a replacement. I feel like due to how old it is, it could break down within the next year or so and that's a pretty big expense for me to get hit with. I was thinking about asking the seller to replace it. What do you guys think? Also, just to note, I was going to pay what he was asking for, maybe I can even ask for a couple thousand knocked off the purchase price? Idk, let me know what you guys think...