I'm taking my Mazda3 with automatic transmission in for 30,000 mile service at the dealer. Twice they've tried to sell me a transmission flush, which I've declined. Question: what service, if any, does the transmission need at this point? Can they just change the transmission fluid? I've read bad things about the flush; are the negative comments about that justified? Point of information: most of my driving is in heavy traffic in DC. Thanks in advance for your replies!

 

I think the flush is basically like doing two trans fluid changes, just in case there are spots of fluid that don't fully drain. Though there may be some gunk that a power flush gets out on top of that.
It may be a good idea since you do city driving, but in general there shouldn't be an issue with just changing the fluid. This is as long as you don't have fluid loss, trans issues, or burnt fluid etc...