I took your advice and tried ADs in Europe, though only two; only one even replied to my request about a discount, but it was a very instructive reply. They would give me the VAT, but nothing else. I believe the reason is that they are selling the discounted ones through grey market vendors (they didn't say so directly, I figured that out after a few other conversations with two ADs here and one very helpful American grey market seller). This keeps their sales up, making GO happy to continue dealing with them, while avoiding the ire of customers complaining to GO or others about unfair pricing. BTW: I've talked to several grey market and AD vendors since your advice (which as you can see I very much appreciated and took to heart), and it's the same here as in Europe, at least for GO watches. Insofar as GO now forces vendors to take more watches than the smaller ADs can handle, they need to offload them to grey market partners.
Are you e-mailing or calling? Get them on the phone. Blatantly asking for discounts by e-mail is not the right strategy. Call, tell them you are interested in a few different watches. Name a few, even ones you aren't really going to buy. Ask them about availability and pricing. Then ask them for best possible pricing on the one you actually want. Negotiate from there.
Try the larger dealers. They will be sort of hit or miss. Almost all will give you some discount. Many will not budge beyond a token amount. But many will play ball and go to the 15-20% range without much effort. Smaller dealers are more likely to clench tight.
The worst people to give you advice about buying watches are people who sell watches.