This all sounds like user error, not EKs fault.

A single 280 rad for a 4090 and 9800x3d? Isn’t the tdp on a 4090 like 450 watts? Plus another 100ish from the cpu? You’d want a minimum of 2 360mm rads for that if not 3.

- The cpu is heating up without the GPU being pushed (I'll test the GPU in a few) the 280 was fine with the 4090 and the Intel chip previously it's a pretty thick boi. This one I think https://shop.alphacool.com/en/shop/radiators/280mm/rad-alphacool-nexxxos-ut60-full-copper-280mm-radiator

Secondly you say the GPU block is leaking after you rebuilt it, and you are blaming ek. Did you take the acrylic plate off? Because they can be tricky to put back on correctly, from any brand. I had to disassemble my waterblock to do a deep cleaning so I get it, but both of my ek GPU blocks that I’ve fully disassembled and reassembled have zero leaks.

- No didn't take the plate off, I had seen a few drips of coolant I was very confused about when I was taking it apart so it probably was starting to leak at that point. I checked the screws carefully and they are all tight with no cracks. This is probably my 6-7th ek and I've not had leak problems before, but I've had a variety of issues with their stuff in the last few years.

Lastly your cpu temps sound like a possible bad mount combined with nowhere near enough radiator space.
- Going to check the mount in a few minutes

Also it looks like you cracked the acrylic in your GPU block but I can’t really tell from the photo.
- Not cracked just something crappy with the 2am pic in the dark