By all means, the dealership should repair your leaking valve. You may have some toilet paper, etc caught in the black tank valve (if it is leaking) or even a defective or damaged seal on a valve. There should be no water/waste leaking when you remove your end cap to connect a hose.
If the dealer can't get you in for repair soon, you can always buy a "twist on valve" to replace your end cap, then just install the cap on that valve. Then, when you remove the cap, there is a "terminal valve" that would stop any flow of waste until you have the hose installed.
Many of us use this type valve as a "last catch" for anything that could possibly find its way to the dump connection.
Here's one type:
http://www.campingworld.com/shopping...on-valve/27868