Excellent writeup motaba !!!!
I will add just a couple of quick points regards to my experience with this,
1) I didn't change the ring seal for the transmission filter. it is a pain to do and is definitely preferable if you can do this. I just didnt have enough room when using the small trolley jacks I had.
2) When originally draining the fluid on mine, it looked like my transmission was over filled by around 1 Litre. (Using the drizzle test). I lost around 500ml when changing the radiator a week prior to the transmission service,
and I noticed the transmission flaring slightly more often. (Hence the reason why I brought forward my Transmission service).
So If you notice flaring, you can always try overfilling the transmission by adding another 500ml above the recommended amount.
3) Another option instead of sourcing the filter and gasket locally, is to use the Cadillac Deep Pan / Wide Mouth filter 6L80 parts.
You will need to source these from the USA, and it will cost something like $180 landed, however the pan allows for an additional 2 Litres of Transmission fluid to be held.
The filter also sits lower in the pan, so it is less likely to lead to cavitation when braking, accelerating and cornering.
Again great write up Motaba
Here are a couple of images which may also help.
Pump that you can buy from SuperCheap
Pumping transmission fluid in to the transmission
Transmission Filler rubber bung thingie
Removing the Sump