MB rotors can be machined. However, it is not worth the time that the shop needs to do so. To do the machining, it takes time... extra 20 minutes per rotors... to set it up and then have the machine cut it for you and then buffing it if you have older machine. You only charge customer like $15 or so per rotor...
For shop with no machine, they farm it out, but that will lock the car in the service bay that you can't use until you get the rotors back.
My experience with machined rotor is that they don't last long... less than
2 years before it warps. Consider that W126 rotors cost about $50 for front and $30 for the back each... it is cheap enough to buy... Of course, that's not the retail price... so double or triple the price for retail. Then this is quite pricy for customer.
As far as changing rotors with every brake job, that is a waste of money and resource. Unless you have something wrong in the first place such as pulsation or abnormal wears on the rotors, I don't see any reason to change it.
The biggest reason for alot of the rotor problems is simply the brake pad. Stick a OE pads in and you will get the same problem again. OE or OEM grade pads are not the best pads. They work the rotors so hard that it eats the rotors in no time. Time after time... everythime I saw OE grade pads on the car, I see abnormal rotor wear.
So what pad to use? Right now, ceramic pads are the best bet... Bosch or Akebono is my choice now. It stops the car good and easily... no black dust. PBR Ultimate ceramic pads are dusty... which is what I got on my car... but everyone else, I stuck in Bosch and Akebono ceramic pads.
Another reason for abnormal wear on rotors... far more common is use of impact wrench on lugbolts... it really screws it up.
Heav... you may have some other issue that cause the vibration during braking.