It is for a leak concern,I am not sure I understand why you are unhappy they took care of you ?
Thanks for the answer Bob4x4, now I know. I realize I should be grateful that they took care of the recall saving me a second trip, but part of my frustration with them is that they didn't inform me of the work or ask if I wanted it done on this particular visit. When I picked up the truck they told me they replaced the tank, but the service advisor didn't know why, just that it was a recall. Come on, pick it up a notch!
I live in the country and they knew I was waiting for the truck. The original appointment was to check/test the right battery which they told me needed to be done before they could replace it. This should have taken 30 minutes. 2hours later they brought the truck out. They hadn't replaced or even tested the battery, only cleaned the terminal/post and sprayed it. The rest of the time was spent replacing the WW tank which I did not ask for or agree to at this time... I had places to be.
Back in it goes to actually test the battery and charging system. Elapsed time: 2. 5 hours! When I inspected the WW tank replacement the first thing I noticed was a big old rusty bolt in the top hole (not from this truck) and a plastic plug fastener missing from my LF inner fender, so it was loose. Add to that the clear coat scratches in the right fender from working on the battery and in the left fender from working on the WW tank... see my frustration! These scratches match the ones on the LR corner of the box nicely from when they installed my fifth wheel hitch and wiring, one more corner and I almost have a matched set! Hopefully this link works:
Death and Taxes TV Commercial - Hagerty - YouTube
I pointed this out to the Service Manager before leaving and he didn't seem to be overly concerned, which is likely why some of his staff lacks care and attention to their performance. He said he'll get some fender blankets and make sure the guys use them. He's the 4th Service Manager I've seen at this dealership in 1. 5 years. Problem is when you live in a remote area with a booming oil economy and they're the only game in town, the customer is stuck with poor service. If I treated my customers like this, I would likely be looking for a job at this dealership!
The guy before me left mad for being overcharged and the guy after me left mad as they had lost his keys and his wife had to bring him the spare set from home.
I'll give at-a boys and credits when due, but these guys just deserve a kick in the pants. Make sure you thank your local service department if they've done a good job for you.
Attention: TDR Forum Junkies 
