Now Deansbimmer is one of
the most reliable sources on this forum, but I do believe that he understated the importance of this. Yes the car will drive for a while, but for $70, this should be a top priority.
I have 126k on my '11 M3, and I drive the balls off of it. I started getting locked out of the odd gears, and noticed a much louder whine when driving in odd gears. I usually change the DCT fluid every ~40k miles (it even came out more of an amber color than black), but I suppose years of sediment moving past this check ball renders it unable to do its job.
If you are changing your fluid + filters, be sure to add this to the list. It's so simple that it's just one additional hex key holding it in place, and you don't have to move anything besides the pan to get to it. Pan, filters, even the cylindrical filter isn't that hard. My personal strategy is the jack up the side with the fill hole, put an extra liter or so of fluid in, then let it down while the car is still running (~2k rpm for 30-60 seconds) and cap off the fill hole then shut it down. Helps to elevate the car or wear gloves.
No more lurching when coming from a stop. Great looking out Deans
first photo is a fresh check ball.
