I have a '93 940 with a frozen left rear caliper. Some of the on-line parts suppliers indicate that there are two versions of this caliper: one with a 38 mm piston and another with a 40 mm piston and that they are marked as such. Other suppliers make no such distinction. When I examine the caliper I do not see either 38 or 40 marked on the caliper. The markings I see include G, 2, 42 and 59. Three questions: If there are two versions of this caliper where do I look to find the identification? Is the piston diameter really all that critical? Are the mounting holes the same for both (i.e. are they interchangeable)? For what it's worth, the existing caliper has two pistons but just one bleed screw. Also, this caliper has already been replaced before, so the unit I am looking at is not the factory original.