The eccentricity of Earths orbit follows a bounded random walk-like pattern, see this chart. I presume most other planets are similar. One could think of eccentricity and argument of periapsis as "polar coordinates"; the centroid of the ellipse would be roughly analogous to "Cartesian coordinates". Either way the orbital parameters are chaotic but bounded.
What causes this behavior? When the orbit drifts away from it's "equilibrium point" what effect "kicks in" to push it back rather than let it drift even further away? Would this picture be qualitatively different under Newtonian gravity (these drifts are very slow so small relativistic corrections may matter)?
My hypothesis is that, due to the smallness of these perturbations, the system is almost linear. i.e Venus and Jupiter will contribute additively to the perturbations (additively in the "Cartesian coordinates" at least), and said contribution is insensitive to the small perturbations for other planets. So we are looking at a superposition of multiple periodic functions; one for each of important enough planet and maybe one for corrections from general relativity itself. Is this line of reasoning valid?