Rear brake problem on F350 - caliper?

2001 Ford F350
$100K miles

In Dec.'06 the right rear tire rim of our truck was heating up after driving. We took it to a Ford dealer and they did the following (quote from receipt):

"found that rear pads were seized in caliper slides, replaced rear pads and resurfaced rotors and cleaned and lubed caliper slides and guides."

For the last 9 months it was fine. Now, the same thing is happening again on the truck - the same tire. The question is: is it worth going back to the dealer to have them fix this and should it be free of charge since it was the same thing before that we already paid for? (The original price paid at the dealer for all brake work was about $800 but that included replacing front pads and rotors too).

Our concern is that they're going to say a new part is needed, and if thats the case, we would rather go to another local shop that is more reasonable, but we feel that since the dealer originally addressed this problem we should have them look at it (also dealer is not that local and about 25 minutes away). Can someone give us an idea on what the problem may be and what the would be? We don't want to pay another large expense if we can avoid it. Any help or advice as to what you think the best course of action is would be greatly appreciated! Thank you.