Z axis isn't level. One end slips down

The X-carriage isn’t level. When I do a Z-calibration, the X-carriage bottoms out at the top and I hear the clicks from the limit switches. But then the right side will sag afterwards. When I measure the height difference of the X-carriage between the right and left Z screws, the right side is about 1 mm lower than the left side. No matter how many times I do a Z-calibration, the X-carriage is always uneven.

When I manually push the x-carriage to the top, I feel as if there is more resistance on the left than on the right. So is there a way to tighten something on the right Z-screw to fix this issue?