Einstein wrote in 1912 :
The principle of the constancy of the speed of light can be kept only when one restricts oneself to space-time regions of constant gravitational potential.
see: https://en.wikipedia.org/wiki/Variable_speed_of_light
Einstein "did not need the ether" mathematically, so he stopped thinking to make it more complex.
See: The CHAMP-GPS outliers.
See CHAMPs-GPS outliers in:
Experiments to determine the mass related Lightspeed extinction volume
around the Earth and around spinning objects in the Lab.
http://vixra.org/pdf/1102.0056v2.pdf
an example: Comparison of the absolute kinematic orbit solution w.r.t. RSO.
Tae Suk Bae, 2003, Ohio State university.
see also:
Reconciliation of GR and QM by a New Gravity-Black Hole and Lightspeed Model Called Quantum- FFF Theory.
http://vixra.org/pdf/1402.0132v1.pdf
The Semi Relativistic Higgs Field Aether with mass related lightspeed adaptation.
http://vixra.org/pdf/1310.0059v1.pdf
See some posters at:
https://www.flickr.com/photos/93308747@N05/albums/72157633500638503
see also:
The O‘Connell Effect in Eclipsing Binaries Explained by Mass Related Light Speed Extinction Distances (Lasof) of Stars and Even Planets.
http://vixra.org/pdf/1409.0164v2.pdf