problem because if you had a stable highly elliptical orbit of two bodies, the attraction would be greater during the approaching phase than the departure phase. The equation would not be balanced. Elliptical orbits would degrade due to the pulling being greater on arrival than departure. This is not the case. Maybe it is only a problem as you approach light speed.

I believe the submitted article gives an example where orbits degrade in just the way you describe.

No, the article describes something totally different. It talks about cases where an orbit decays because the gravity is felt at a different location from where you expect.

As I mentioned in a different comment, that's not what happens.