refurb'd an original MBA
broken sound, and extremely slow, suggesting disk errors, short battery life
Replaced the audio card and cable, battery, and the HD (with a SSD from a different vendor, because you don't carry a drop-in SSD replacement). It came up working fine, installed Ubuntu 12.10, works great.
Be slow and methodical and you won't have to take the case off to install the new sound card you forgot to put in.