I don't understand what you mean by grey market Dianas if Umarex are the official Diana importer for the USA. Grey market products are usually imported after they have been purchased from a source in a part of the world where the retail price is lower than here. They have no warranty because they are technically second hand and they circumvent the the manufacturer's distribution and world pricing plan. It goes against the manufacturer's desire to charge more for products in rich countries than poor countries. Isn't the Diana warranty taken care of by Umarex?
Not that it matters, airguns are items that should probably not be owned by anyone that can not repair them.
Red.