The manual doesn't really give a regular replacement schedule because the transmission is sealed and is supposed to be "lifetime" fluid; however, it is my opinion that the fluid needs to be replaced at least every 75,000-100,000 miles. The manual does give a schedule in the "severe maintenance" schedule section of 60,000 miles for the automatic transmission and 75,000 miles for the dual clutch transmission. I replaced mine at about 120,000 miles and the fluid was extremely dark, almost burnt so I suggest replacing it much sooner than that. It's normal to have the fluid be a dark red, but not black. At 41K, you are probably okay letting it go for another 20-40K miles.