Front brake caliper rebuild.
 

I am rebuilding my front calipers (non S 2000 model) on my boxster and ordered the 36mm 40mm kit as everything I have found here and online says that is the piston diameter for each caliper. My Dad currently has my calipers and is rebuilding them but says that the larger diameter dust shields and seals do not fit and that it appears all the pistons are the same size (36mm?). I do not have the calipers in front of me at the moment to verify but he has been successful using the smaller parts from the kit to rebuild at least 3 of the 4 pistons in the first caliper. Is something off here or are there calipers with 4 36mm pistons in each one?

Just thinking loud, since the caliper repair kits are not really expensive, perhaps check with the Porsche dealer (by providing your VIN), they could recommend the correct seal kit..?

From factory, all 986 have 40/36 front and 30/28 rear. Also, it doesn't really make sense to make calipers with equal size pistons. The staggered size is there to reduce tapered wear of the pads.

Yes, you are correct...
 

I picked up the calipers this evening and my dad was comparing the size of the pistons with the 36mm inverted over the 40mm or something and the lip was making them look the same size I think. I could plainly see the difference between them, but he had trouble seeing the difference...disaster averted and the rebuild process continues.