What exactly has failed? This is an item constructed with TPR, which is very sturdy with many of the same attributes as silicone. If not the dong itself, did the bullet accessory fail?

Woops...that's TPE, not TPR...same attributes.

yes, the bullet vibrator has failed in both of the Gia Darling's we purchased. Neither lasted more than 2hrs of total use before the vibrator quit working

Not typical, but I guess that could happen. link is our Warranty company, and for a small fee to handle shipping and handling, they will replace it for you. If you purchased this from Eden, I also bet they could steer you in the direction of a higher end, multi-function bullet that would last a whole lot longer. While the ones we include with vibrating products are normally adequate, they just don't have the advanced features like our Xtreme Pack bullets, which have much more electronics built in for multiple functions of vibrations. Since you like the dong, it may be a wise investment to get into a better piece of electronics to go with it. Just my 2 cents!

I wasn't aware that the vibrator quality is a selectable option in a molded unit, it certainly is not replacable without damaging the toys

Actually, you don't. These products are made with a double pour process. The outer skin is poured into the mold, then the bullet is placed. The second pour seals the bullet inside, and creates the suction cup base. The bullet that we use in these are heavy duty, and our best selling unit. Numbers-wise, the failure rate is very low on these...just your luck to get a couple duds..usually when they do fail, it is the battery pack and not the bullet motor. These bullet motors are the best made RoHs standards(European) and CE approved. My best suggestion is to seek warranty replacement at our Warranty company, link. The other option, which is your call, is to try wiring another control to the wires, but by the time you buy one, connect it, be sure the wires are well connected and taped, you might as well replace the whole unit. The shipping/handling charge is less than it would cost you to try and fix it, and you would get a new item. I would also suggest that you look at some of our sleeves that are made with the same Pure Skin material, that slip over a vibe...if the vibe dies :-(...you just need to buy another, and the sleeve is good to go. We sell a Futurotic Penis Extender (1626-01-3), the Adonis Extension (1625-25-2) and the Futurotic Penis Extension (1620-00-2)...all of which were made as a male extension, but also slip easily onto a standard 7" or 10" multi-speed, or multi-function hard plastic vibrator.
Just a thought.