My right front caliper piston won't compress so I can fit the caliper with the pads over the rotor. It is a 2010 g37x coupe please help

it's the front driver side

 

If you have an old set of pads insert one and use a c-clamp to compress the old pad against the pistons, or a piece of wood will work too, unless the piston is seized

 

I used a clamp on the pad, what could cause a piston to seize? a ND what would I have to do? buy a new caliper?

 

Did you open the reservoir cap before trying to compress the pistons backs?

 

not at first but then I did, I was switching out the wheel hub and took the caliper off, tied it off to keep pressure off the lines. when I went to put it back on some brake fluid leaked out of the boot, did that have anything to do with it?

 

So I took the caliper completely off, drained all of the fluid hit the piston with a rubber mallet and broke it loose. checked the seals they were fine put everything back together and it's working fine.

 

Glad to hear.
Next time you may want to remove the piston in question and get a 3m pad and gently scrub around the piston sides, may have some corrosion that's causing it to hang up a bit.