I am selling my Stax 507 because since I got the O2 Mk1 I have not been using the 507 much. I am upgrading to the SR-009 in the near future, and the 507 has to go.
The original headband is broken by the previous user, and has been replaced with a much more comfortable Lambda Basic Frame, which cost $150 (http://staxusa.com/Parts/Head-Band/STAX-Basic-Headband-Assembly.html). If you know Stax headband, there is a small piece of plastic screwed onto the headband, which clamps down the leather band. The plastic piece is missing on the original headband. The original headband will be included, and you can fix it if you want.
Most people I have asked prefer the sliding mechanism on the basic frame as compared to the newer clicky mechanism on the original frame in terms of comfort.
Serial number SE1-1281. Bought new from Japan November 29th year 2010.
I accept payment through Paypal gift. Buyers pay for shipping.