At 40K, I'd definitely do it. Better a bit early than late, especially if you don't plan to pay a dealer an arm and a leg to activate the pump to drain the cooler. No need to before your fluid is nasty. I'd probably do it at 30K the first time. I'm doing my 6MT at the 2-yr mark, even though it'll only have about 8K. I want to make sure level is right, and that the right fluid is in; I immediately felt a change for the worse right after the 1,200-mile service. The good news is 6MT oil is MUCH cheaper than DCT
, but in both cases is just 2 liters for a drain and refill, so not bad at all. Changing DCT oil is just like 6MT (drain and fill holes), with the exception DCT has to be running (both have to be level) while topping it off, like most auto trannies. The procedure is somewhere here (or on another thread; just search). There's no converter to drain, so once you have the right oil and a way to raise the car level (easy with 2 ramps, 2 jack stands, and a low floor jack), it's pretty hard to screw up the oil change if you know what you're doing. Good luck.