uneven front/rear brake applic W124
 

1995 E320, 207K miles.
Over the past 2 months the car was up on ramps while I worked on the engine. Engine work done, I took the car down, started driving...there was a lot of oxidation/rust on the brake roters. I figured normal driving would wipe them clean and smooth.
After 120 miles the front brakes have more or less cleaned themselves but the rear have a few high spots where they are clean and the rest (majority) is still rusty. Driving/applying the brakes are loud, rumble and pulsate.
I realize the fronts get more action than the back but I thought it was more along the lines of 60/40 or 66/33 ratio but it looks like my backs are barely getting touched. On my Chrysler vehicle there is a load balancer that controls front and back brake application, I don't believe there is such a thing on MB's.
I sprayed brake cleaner on the rotors which helped visually but didn't fix the rumble and pulsating.
I figure the fix is to shave the rotors down if they are within spec. The back brake pads have 70-80% meat left in them, the fronts have to be replaced within the next 3-4000 miles.
Any comments?

Most MB's use a 70%+ front braking.

Possibly the rears on your car have calipers that aren't functioning properly. RUST?
For rust issues remove the pads & use wire brush on the mating surfaces and apply never-seize.

Also are the rear pads OE or aftermarket?