Sticking Brake Piston

I was changing brake pads on my new-to-me dirt bike (KTM of course) and discovered that the lower piston in the front caliper is sticking. I can push the top piston in by hand and the brake lever pushes it out. It takes a piston retractor tool to push in the bottom piston and squeezing the brake lever won't push it back out. It's strange because the pads and disc are worn evenly.

Any suggestions? Am I just fooked and need a rebuild?

I guess I could use a block of wood and a clamp to hold the top piston in place and see if I can move the lower piston with the brake lever?