First of all there is absolutely no reason to drop the pan to do a drain and refill. To do so makes no sense since you cannot clean anything with an integral pan-filter.
I agree about draining and refilling and always remove the refill plug first just in case. I also agree that doing this at 50K can be done two to three times before dropping the pan and replacing it. You also need to know that Lifeguard 6 and Mercon SP will work as fluids for your ZF transmission but no others unless you wish to experiment.
I sent Blackstone samples of both and they reported that both samples minus smell and color were identical and could have come from the same batch.
Mercon SP can be sourced at O[Reily's for $4.99 a quart and LG6 in a 12 L case for $200 plus shipping.
I did my first change at 38K sent the sample to Blackstone and they stated that the fluid had material in it all normal and nothing unusal and has a lot of life left. Once I get a scanner working I will post the results.
When I drained the fluid out it was darker in color than the honey colored LG6 but nothing special. All LG fluids smell bad and this was no different used thus nothing there.
I could have easily gone to 50K but I am anal and will change before needed since my BMW transmissions go well past 200K before they fail.
Hope this helps, the tech is partial right on his advice but dropping the pan is a total waste of time until you replace it...