Q: Feel lurching sensation under brake pedal.

Hi there. Were the brake pads on the rear replaced or only cleaned? When gear oil leaks onto the brake components long enough to feel it in the pedal, then the pads are pretty saturated as well. As with any used part, the history is generally unknown; it could have a bent axle from a previous accident or simply have had moisture in the unit that has now affected the bearings. The front brakes could be at fault as well; does the steering wheel shake when you hit the brake pedal? If so, then this is a sure sign that the front brake rotors have excessive run-out and need to be replaced. I suggest having a qualified technician perform an inspection to avoid replacing unnecessary parts. Your Mechanic has several available technicians that can assist you with a brake pedal shakes inspection.