If a tranny flush is what I suspect it may be, you may be better off doing nothing. The reference to being worse off is what happens if you leave the oil change too long. The tranny then needs dirty oil within for it to function. Clean oil is too slippery in a worn out tranny. The quick fix for any tranny that is slipping or shifting rough is to add iron filings to the existing oil - that will carry the vehicle until it is off the car lot. Well actually iron filings do not work so well in the ZF as electrically conductive oil tends to throw off the operation of the Mechatronic - in other words, the ZF is not a fancy Powerglide.

What I would suggest is that one stay away from any of those chain transmission shops. They are perhaps good with GM Powerglide and like, but that foreign stuff - well ask them if they can even pronounce Zahnradfabrik Friedrichshafen let alone spell it; for starters, try them on Mechatronic. If however, they answer Ferdinand Graf von Zeppelin, as in airship, I would regard that as a pass.

Anyway, the link below has some material re the our ZF 6HP26 tranny.
What is generally done is either a new pan/filter combo and near ZF LifeguardFluid6 oil or what I would call just changing the transmission oil, old style, again with LifeguardFluid6 or the LR spec oil which is I guess the ZF6 oil with the addition of Unobtainium and Stardust - well it is priced that way. At any independent, you are looking at minimum eight hundred dollars for a pan filter and oil change; the dealer, about twelve hundred. If you find out the name of the independent your dealer subs the work out to, you get the eight hundred then. Most often, that independent, (located in the east end of town), will have a flock of dead Mercedes, Audi's, and Beamers strewn about - as such, you know that is the place.

This flushing procedure of the chain shops, using some kind of vacuum cleaner / pump, I think that is best restricted to Powergides and the like.

DISCO3.CO.UK Photo Gallery - ZF 6HP26 Automatic Transmission in LR3

 

My tranny oil change was about $500, at the dealer...but they didn't do the pan/filter.