Try some WD-40 or Liquid Wrench instead. If you don't have either some penetrating oil will help. Tri-flow, sewing machine oil, pull the dipstick out of your car, and drip some oil on the screw, any lubricant will be better than the degreaser.
The citrus degreaser is a solvent, probably has a fair amount of water in it too. On my Thomson stems they use screws with a black oxide finish. They also anodize their stems. Anodized finishes are oxide layers too. The oxide layers are similar enough that they stick together. I have a feeling the citrus degreaser might have cleaned off some dirt, but sped up the two oxide layers becoming one. That might not be entirely correct, but anytime I put black oxide screw into aluminum parts I have problems.
You need some lubricant in between the threads of the screw and stem.
To break the screw loose you can place an Allen Wrench in the socket head screw and give it some sharp whacks with a hammer. Not really hard, but sharp and quick. Doing that can break down the oxide layer fusing between the stem and the bolt.