I am thinking of changing my ATF fluid on 2009 DB9 Automatic with 20K miles.

Recently I changed my 2006 BMW 750LI ATF fluid, and when I saw what came out I am convinced that this shell ATF 1375.4 fluids are not LIFETIME.

I think 750Li and AM share same or similar Transmission box made by ZF. In BMW one changes ZF Trnasmission oil Pan which contains built in filters.

so my question is
1) should I change transmission fluid with the pan?
2) can someone help me source it?

there are transmission oil sump pan on sell at Aston martin car parts.com but they are bit expensive, I was able to get one for BMW for $ 93 (from FCPeuro) with shipping. If its the same why not use that?, its made by ZF

 

It's a different transmission than in BMW:
Aston Martin's Touchtronic II gearbox is actually a comprehensively re-engeneered version of ZF's excellent 6HP26 6-speed automatic transmission. This was originally designed to be bolted directly to the engine at the front ot the car. With the DB9's clean-sheet design engineers wanted to place the transmission at the rear of the car for better weight distribution, but in order to use the ZF in a transaxle layout they had to design an all new diecast casting, create a completely new mounting set-up, while also incorporating a differential into the unit.

 

You can get the pan from Land Rover (ref LR007474), the oil is ZF Lifeguard Fluid 6,you will need to remove the right hand exhaust pipe to gain access to the filling plug.