Volvo Repair: Transmission fluid, volvo dealer, fluid changes

Question
I have a 2003 S40 with an AW55 automatic transmission and 22,000miles.  I like to maintain my cars with fluid changes but my volvo dealer says "lifetime" fill and not to mess with the tranny.  They don't even carry volvo atf saying they never need it and it they do, they use DexronIII/Mercon which seems to be not appropriate for a tranny requiring JWS-3309.  Can I use Toytota T-IV fluid which is also a JWS-3309 fluid to do a drain and refill?  Mobil 3309 seems to be also an option but I can't find it.  Thanks-Bill

Answer
well some of the transmissions use dextronIII this would be the AW50-42 ,THE AW55-50SN TRANS uses a special volvo fluid not the dextron fluid.it could be similar to the toyota fluid but I am not sure.a drain and refill will require 3.5 quarts.the volvo fluid is about 75 dollars for 1 gallon of fluid.