There are multitudes of comments and videos on this contradiction... Comments below to help me (and others in the same situation) to navigate in order to make a decision.
Most dealers will advise against touching high mileage transmissions with no history of fluid changes. This seems to be related mostly to liability issues in case a dirty/worn transmission dies after a flush or fluid change. Hard to explain to the customer what may have happened. So they just refuse to do it, or charge unrealistic prices to deter you or to cover their ass.
Until about 100K miles in my car, I was on the fence about taking BMW's "lifetime" transmission fluid statement seriously vs the ZF transmission maker's 62K miles guide. Since then I have been reading up on it, and this is what I gathered one is facing with a 113K miles (183k km) car...which is already 83K km's over the ZF's service limit.
Do not flush, unless you replaced your transmission fluid every 30k miles or so, or you usually drive on mostly highways at moderate speeds. A dirty transmission would not benefit from a flush as the dislodged sludge and solids may clog the delicate oil passages/solenoids. So, you should know your car's history.
What about changing it when already over 100K miles? The best (insurance) would be to take a sample of the transmission oil, and send it in for analysis. If it comes back fairly healthy then changing should not be an issue at all. In a normal transmission oil change (vs flush) you are replacing at a 70/30 ratio (70 percent new/30 percent old remains).
I plan to replace my fluid this month. But will not do an oil sample analysis, because I believe that my transmission is fairly spared from abuse. The risk of letting it go forever without a fluid change is much larger vs doing it now (in my opinion).
I bought my transmission fluid service kit from FCO Euro a year ago. The fluid change is actually not that complicated, there are some traps and cautions to obey. The largest risk I am facing is to get the car securely high enough to be able to get under safely and comfortably enough to do the job. As I am getting older, I am realizing more and more that a few tons of metal toppling on me is quite detrimental to my health.
Attached my notes I gathered from various sources and the official ZF procedure files.