it all depends on the problem with your mpc.
if the problem is repairable, they will repair it.
if they can't repair it, you'll get a replacement. but depending how long you've had the unit, you might end up with a "b-stock" unit which may be less than desirable.
if you're looking to send it in for a replacement just to get the pad fix upgrade, they won't do that. they would most likely just replace whatever individual pads that have gone defective.
so my advice to you is if there's nothing wrong with your mpc, then don't bother sending it in. you'll only waste your time and money on shipping + insurance.
don't damage your mpc intentionally just to get a replacement. that will void your waranty if they see that. then you'll be sh!t out of luck.