I'd suspect brake adjustment right off, but it could also be a bit of condensation [w/ maybe a wee bit of fluid film] has "glazed" things - I'd "ride" the brakes a bit a few times to see if they'll clean up w/ the heat, then if adjustment don't fix it, pull the drums and take a look - if there's no real leak, maybe a little scuff w/ sandpaper would fix it up
Bill
