2005 Beetle Convertable

I have a 2005 Volkswagen Beetle convertable. The dealer told me a valve must be replaced. The valve distributes fluids. The car has been bucking at certain times and they say that is the problem. Is the valve located in the transmission? The transmission is sealed therefore my regular mechanic can not fix it. The dealer wants $1700 to fix it and needless to say, I really don't have that kind of money. I also complained saying that the car is only five years old and has only 40,000 miles on it. The dealer said they would talk to the volkswagen rep to see what they could do in terms of price. Is this something that my mechanic can fix? Is a price of $1700 warrented and should this part have gone bad already? Any help you can give me would be greatly appreciated.