100% your getting taken for a ride here (in my opinion). No way it costs $1640 for a R&R of a valve cover gasket. I just did mine a couple months back in my own garage.... parts (VC, new aluminum bolts, gasket) were about $250 and it took me about 2 hours to complete taking my time.
I'd get some concrete evidence of where the Transmission leak is coming from. Is it from the pan, ? Filter? Sensor on top? all of those are pretty simple talks to complete.
I just did a complete service on my DCT as well and again, parts were about $400 and another 2 hours taking my time.
I get not everyone is a DIY'er, but that's robbery in my book.....