I bought the official ear pad replacements for my PXC450 back when those were available, for 1/4 of what the headset cost. They are so terrible that I stopped using the headphones entirely. I lost faith in Sennheiser after that, now I just use cheaper ear buds.
I bought the $21.99 Chinese replacement “Sennheiser” pads from Amazon. Straightforward to replace (though not trivial). Very comfortable. My headset feels as good as new.