Think you did the right thing.
The 33xx models have an unfortunate reputation for being somewhat temperamental. Given that the seal on the back is broken, it would be hard to convince me that it wasn't a returned and refurbished model. Though the warranty should still be intact, I still wouldn't accept that on a new watch and definitely not on a 33xx caliber watch. A service from Omega is certainly a good idea, as the dealer himself isn't even authorized to simply put a new seal on the watch - defeats the whole purpose. If you're sold on that particular watch sending it back was probably the best option.
Omega will presumably check the function, operation, and water resistance before putting a new seal on, which from the service center is typically blue, not red.
30% discounting isn't unheard of on current production models either, but is better than some.
