I just use the comments section on fuelly.com to track maintenance. I already use fuelly.com to track gas mileage of bike and car.
If you do use a spread sheet be sure to store it on Google Drive or Microsoft OneDrive or storage cloud, as well as other important documents. That way you can access from your phone or multiple computers and won't have to worry about loosing it if computer is damaged or stolen.
Actually the best way would probably be a google spread sheet. This is a spread sheet app on the web with web storage. You can access via any device such as phone or computer.