My Air had a dead battery and problems with the I/O unit. After five years I thought I should buy another one. A shame, because the Mac worked perfectly.
The new battery and I/O unit arrived in only three days from USA to Spain, and I followed the instructions to repair. No problems. The Mac lives again and I think I will use it five years more.
I had lot of work to find out what model is my Air. A guide or page in FixIt to know the models we have would be useful.