Remember that whoever you get to cover your drive train under warranty, they will want some type of verification that scheduled maintenance was performed. They may not accept your assurance that the proper items were attended to on a timely fashion like a certified shop would provide with an invoice and worksheet.
I am sure that you probably do the work better than most shops, which is why I do my own service, but I am just saying you need to make sure that whoever you get for an extended warranty understands that YOU do the scheduled service. You may want to get it in writing if they will allow it.
