So TVS will never need a rebuild.
The service interval on the Eaton blowers is 100,000mi. So yes, at some point they will need to be rebuilt. But not very many blown cars make it to 100,000mi. And if you are running a M122 you can simply buy a replacement blower for $400 and swap it on in about an hour.
The Saleen service interval is 20,000-25,000mi. It costs about $1000 plus $200 in shipping for a rebuild, you will be without a running car for a few weeks and it's a PITA to box everything up for shipping.
If a used Saleen blower is purchased and it has not been recently rebuilt chances are that it will need to be soon. So the cost of the rebuild ($1200+) needs to be factored into the price of the blower.
Yes
What exactly will need to be rebuilt in a well maintained Saleen, that will rarely need to be rebuilt in a TVS?
Everything that spins, moves, meshes or seals.
Eaton blowers are designed to be used in OEM applications. The OEM's have MUCH higher standards than the aftermarket when it comes to durability and quality.
All of the aftermarket blowers, Whipple, Kenne Bell, Saleen, etc, etc, etc need to be serviced a LOT more than the Eaton blowers do.