I have a MDR-CD900ST and several MDR-V6 units. The pads all fit each other, however, recent pads are different from older pads. The older pads as found on Japan made MDR-V6 and MDR-7506 are not as deep as the pads on the newer Chinese made counterparts. I do not know if the Sony replacement pads being sold are being dispensed from the old style or new style(as found on the Chinese units). The deeper pads on the newer Chinese units creates a more uneven sound, in my perception, by a substantial degree. At first I thought the Japan units sounded different from the Chinese units, but I switched the pads around, and bingo.... the pads are the difference from what I can tell. However, you can probably flatten the pads using some constant pressure in very hot water(almost boiling) for 30-60 seconds. I corrected pads for a different headphone in this manner once; I expect the same thing would work here. If you do this, be certain to use cloth/towels between the metal pan surface and pleather surface of the ear pads.
Chris