I own a MC40 that has a decal JCWorks on the dash. I was looking at brake parts and I was wondering, should I be looking at the John Cooper Works parts or just Cooper S?

 

The MC40 did NOT come from the factory with a JCW Brake Kit.

 

Yes, unless you've changed them, you've got the standard brake parts. Easiest way to confirm is the "JCW" brakes will have red calipers.

 

No red caliper, so that answers that. Well at least the parts are cheaper.

If the brake sensor light has not come on yet, do I need to replace it anyway, when I do the brake job?

My mechanic wants almost $700, to replace the front discs and turn the rears. He says I have about another 3 - 4K left. Can I get away safely, by just replacing the pads, without replacing the fronts discs and without turning the rears? I have 37K on the car now.

 

Most definately not, the dealer tends to try and charge you for it though, so if you don't get one make sure you're not charged. (Common practice for dealers to charge for it when they do the job, not replace what doesn't need replacing and store the parts and save $$$ that way.) If you're going DIY I've been quite pleased with my Cermaics from Advance Auto. Be sure to pick up the Harbor Freight tool if you're doing the rears on your own, it also makes the fronts go by in record time

And it's a good idea to change out the fluid while your at it.

 

I've had the fluid changed and while I was there(independent shop) they said that I will need a brake job, with the details I mentioned above.
If I go Ceramics, the pads will last longer at the expense of the rotors, whereas if I stay with non ceramics the rotors will last longer.