The model number on my Superba oven is KEMC308KSS01 and I just installed parts AP3137553 and AP3082257. The door still feels just as heavy. Did I not get the correct replacement parts?

CHSDIVER

See UPSDave's post above. He has a link on where you can purchase the part. The price is reasonable. I would buy two.

Replacing the spring isn't very difficult if you're mechanically inclined.
You're basically removing a few screws, the front panel of the door is removed exposing only the glass part that's still hinged. The springs are exposed. Hopefully one spring is still in tack so you can see the orientation of how to put the replacement in. It's not very intuitive on how to do this part.

Below are some notes I've saved from a forum that used to be on another parts supplier's website but seems to gone now. Not sure what happened to that forum. It was very good. I've been contacted by several people on how to replace this spring. You are not alone out there.

I recommend you order both springs first and have them in hand before you take it apart. First time doing it will take about an hour. First you take the vent grill out between the oven and the microwave, then the screws that hold metal plates at the bottom of the door, then two screws on the inside of the door that hold stainless panel to the assembly, then the screws that hold the large black plastic filler, leaving you with glass door still attached to the unit. The hinge area is now exposed, which the spring is more of a torsion bar. There are two going in opposing directions. Click the spring in place, open and close the door a few times to make sure all is well and then reassemble.

If you do not have any distractions and put the screws in piles for where they go you should not have any problems. You never remove the glass or the seal so there should not be any seal issue.

My micro/oven combo was slightly differently, so I ran into a snag with the exhaust vent that comes out between the micro and oven. Had to remove a screw on that so I could slide it over to get to a screw for removal. The screw is on the inside of the duct, hard to get to, and unnecessary since the duct is help in place by the front grill.

Another snag I ran into was putting it all back together. The location of the screws is another design flaw in terms of support. The door seemed very flimsy in how the cover fits back, but that's the way it is.

Good Luck!