It's not uncommon for the calipers to stick to the discs when stood idle. And they will let go with a bang. I think it's very doubtful that the seals have gone. Calipers rarely leak, even when they get old. Wipe the rim and see if you can make out what it is, but it might just be condensation. Go for a good run and get the brakes hot, then keep an eye on them, and see how it goes.
