I learned about the risk of fluids "the hard way", that's why I wrote my previous post to prevent other people to make the same misstake.

I wrecked one driver because I used too much alcohol on a cloth to clean the outside of the cup while the driver was still inside. There are two tiny holes next to the "headband-connecting-ball" which lead with small "pipes" to the inside of the driver, supposedly the "bass reflex pipes". After...

OK thanks Ash. I bought a beat-up HD 250 I with working drivers but unfortunately I wrecked one of the drivers while cleaning it :-(. If anybody has a working HD 250 I driver for sale please let me know, I only need the "bare" driver basically. By the way the aluminium rings I bought from you...

Are the drivers in a HD 540 I or II the same as in a HD 250 I or II and if not how can I identify them?