I was able to contact Sennheiser today regarding parts. The drivers for the HD-558 actually have two part numbers that are off by one digit. There is a driver for the Left, and another for the Right. The cost was just a few cents over $41.00 for each driver. Shipping was a flat $6.50, based on any number of components ordered. The drivers are out of stock in the U,S. until sometime in late-February. I wasn't 100% set on replacing the drivers in my HD-555 at this time, so that wasn't a biggie. I did order new ear pads for about $27.00, with shipping included. Buyers in New York, California and I believe, Illinois will pay tax on their purchase.
As to the $41.00 cost per driver, plus shipping, I can look at this in a few ways.
- When I was buying the Magnum drivers for the Grado headphones, I was dropping about $130 - $140 for a pair of drivers at the time. Are both comparable? I'm not sure. I'd have to measure both again, to check the sizes. I think the Sennheiser price is actually pretty good. Grado doesn't sell drivers, so you have to go with the Magnums, or buy used drivers off the forum if you need them.
- When you add up the driver costs from Sennheiser, plus a pair of ear pads, it gets you up near $110.00. However, on Amazon, you can get Sennheiser HD-558 headphones that were returns for about $115.00 and $6.00 for shipping. This provides nearly new head pieces, cups, cable, pads, headband and the drivers for the cost. So, it might be better to keep the former Sennheiser running the existing drivers and add a pair of HD-558s to your collection, if you so desire.