2003 deville coolant crossover leak
 

I just bought a 2003 Cadillac Deville. I got a great price on it because it has a coolant leak. I can't see it, but it will go through all the coolant in a few minutes. The gentleman I bought it from said the Cadillac dealership quoted him 550 for the crossover, 520 for labor and about 100 for the gaskets if they need to be replaced.
It is my understanding that it is the crossover that is the problem.
1 is that a good price? Could I find someone to do it cheaper?
2 is it common for the crossover to crack or go out before the gaskets?

It has 192k miles(a good chunk are highway miles). Serviced regularly. Engine and transmission are smooth and don't seem to have any other problems.