First off: Apologies if coming off a bit antagonistic. I appreciate the product and the niche it occupies, and the work you've done to get it here. Should have been more constructive in my approach to feedback earlier.
Than said, I would look into either extending the cold plate or pump screws to extend through one plate to thread into the other as an easy way to add additional clamping force, at minimal risk to the integrity of the acrylic. alternatively, add a screw from the top under the pump as seen below, though this risks potential for cracks with the small amount of material between it and the pump opening. less ideal of a location to install into.
While I may be an aerospace engineer, all orings regardless of usage case require an even clamping force to seal properly, which is the root of my concern in the design lack of even clamping and degradation over time increases the risk of a critical failure in the area with less clamping force. given this is using a Class I oring, with a use life of around 3 years, I felt this was a reason to be concerned that failure may be seen earlier in its lifespan, risking hardware failure.
I plan to modify mine at my own risk, as I believe it is still a good product for use, with a minor modification, but as a whole yes would I have been wholly unsatisfied a return would have been sought as that is the correct course of action rather that a (see above) admittedly overzealous post on a public forum.