If you describe how the sound varies it might help diagnose. Is it “wow”, i.e. frequency change up&down, “flutter”, i.e. rapid tone or volume changes, “thinning” i.e. certain frequency ranges but not others fading out, or additional non-recorded sounds added to the mix?
Warped records might cause frequency changes, but it is usually small. Big warping sounds will be bumps or skips from the cartridge bottoming out. Vertical tracking angle changes can cause the sound to change, but it’s not so obvious. An off-center hole in the record pressing is more likely to cause wow, but is also easily visible from above looking at the tone arm wobble in and out.
At this age and with multiple new records, I would bet on mechanical failure of some kind rather than merely warped vinyl, but hopefully an expert on RX2 restoration will chime in if there exists some obvious failing…