Binding OSF Caliper

[steamship]

Have an intermittent issue with the OSF caliper in that it appears to bind randomly. So far it has only happened twice, once before Christmas and then again at the weekend. Both times, I was on short trips on an A road doing around 50mph. On the first trip (around 12 miles), I started to notice the car vibrate ever so slightly, and just put it down to the road condition and running on winter tyres. I stopped at around 15 miles, and when I got out, I could smell the front brake. It was also hot to the touch. All the other were fine. I left it for about an hour, and the trip home was fine. Something similar happened at the weekend, although this time I stopped earlier, and would like to get it resolved ASAP.

I've done some searching and I've found a couple of options. The first is that the pistons are corroded and I need the caliper refurbished, or a new one. The second is from a comment by Zip in another thread:

"You may well have the classic corrosion problem under the stainless plates at either end of the caliper that the pads track along. The corrosion lifts the plates proud of the caliper body, and can stop the pad fully retracting when you release the brake, causing the pads to drag on the discs and over heating them."

For option 1, would there be any issues with only replacing one caliper (new or refurbed), and for option 2, does anyone have any pictures showing these? I've checked the Service Manual PDF for the braking system, but it doesn't show these plates.

Finally, the PDF shows that there are two different types of HP-2 calipers, steel and aluminium. Short of taking the wheel off, any idea how to identify them?