You may want to check with "The Man" who has specs for all this stuff but I beleive that the MSP caliper is the same as the caliper from an ES. The cage, or the part that holds the brake pads is the part that is different....may be able to get an ES caliper easier from a junk yard or rebuilt from a parts store than an MSP caliper....then just change out the cage part.....just my 2 cents....
I do believe the MSP caliper is larger overall, but do check it out and see if you can rebuild it using a regular Protege caliper instead. It would be a LOT cheaper..
