So after months of thinking that my heater has been blowing out cold air, It has come to my attention that cold air is only blowing out of the driver side, but the passenger side is blowing nice and warm. Anyone have experience with this issue?

There are 2 heater valves on the firewall. One of them is likely stuck. The operating cable and heat control lever may also be damaged.

Funny you mention this now, I had the exact same issue on my W111 Coupe and I sorted it out yesterday. In my case the screw holding the lever (actuated by the handle via a cable) on the heater core vane was loose. So the lever was moving ok, but was not actuating the vane behind it. It was just a matter of tightening the screw. Assuming youn have the same heater unit, These levers (one for each side) are at the bottom of the heater unit under the dash. Make sure the levers are pushed to their maximum clockwise when you tighten the screws.

Thanks guys, I was finally able to take a look at my heater levers. I seems that on one side the screw has loosened and on the other the screw came out altogether. Does anybody know where to get another screw?

I would start by looking under the carpets as that screw may not have gone very far. Otherwise I would take the other one out to see what it looks like and try to find a similar one (metric) in a hardware store.

same threads as a spark plug top