my trans fluid was darker than usual and I went in at nearly 70 thou KMS. I had to get some other work on the tranny done and I just had them drop and flush aswell. I did not have any issues before, but it sure was smooth when I got it back. Could barely feel the shifts after getting flushed. I would read the manual and see when it is recomended or just decide to get it done and stick to a regiment, every 40 thou, 50 thos, 25 thou whatever u choose but just start doin it