You can get 'rubber grease' that is compatible with various grades of DOT fluid but I was always taught to use a little brake fluid only and that was the instructions with the last rebuild kit I had. But I am an old ferret
+1 for a little red grease behind the piston seals as this is where corrosion can get hold-pushing the seal out of its groove & making it bind onto the piston to hard=seizing brakes
regards