How often should the fluid be changed?
Under my owners manual 'Practical Hints', page 343 it states: "The transmission has a permanent fill of automatic transmission fluid. Regular automatic transmission fluid level checks and changes are not required. For this reason the dipstick is omitted. If you notice fluid leaks or gear shifting malfunctions, have your [dealership] check the transmission fluid level."
That being said, most long term MB owners want their transmission serviced, and many on the forum think the 'transmission sealed for life' concept is not in the long term interest of the mechanism.
I asked my local MB dealership Service Advisor what they recommend to help prolong the life of the 722.6 transmission, and they stated a fluid and filter exchange every 40,000 miles would be beneficial, coupled with an adapter replacement. That being said, MB dealer ships use the ATF designed for the 722.9 transmission when servicing the older 722.6 transmissions. Not my preference, but it is allowed by current technical data. http://bevo.mercedes-benz.com/bevoli...&language_id=1
The 40,000 miles interval along with using the original spec ATF is the approach I take. However, everyone makes their own judgement and gets to live with the results.
Here is the English from German translation of the service bulleting 'clarifying' the sealed for life position described in our owner's manual.
New M-B bulletin, re: 722.6 & 722.9
In march of 2003, M-B released a bulletin, advising a one-time-only transmission fluid change @ 40 k miles.
This is to remove any particles that may have accumulated during break-in.
At the same time it is also advised to change the fluid on the 4-matic transfer case
Circular PW NR. 44/05 NFZ NR. 20/05 24.03.2005 to all Mercedes
Introduction of the transmission oil changing with automatic
transmissions 722,6 and 722,9, as well as with the transfer case of
the 4MATIC-Typen 203/211/220 uniquely with 60.000 km.
Ladies and Gentlemen
A substantial criterion for the customer satisfaction with
automatic transmissions is the switching quality. This not only in the
newer status of the transmission, but constantly over the entire
After the introduction of the optimized lamella package in the
transducer bypass clutch (increase of the number of grooves on 72 to
02/2004) to the long-term stabilization of the switching quality, as
well as, the oil change represents a further step to the conversion of
the NAG1 to the oil used with the NAG2 for switching quality
optimization, in order to hold the switching quality also with high
run performances on a high level. In the oil stored particle is
removed by the unique oil change, whose entry takes place to a large
extent into the first 40'000 km and it can have impairments of the
comfort of the switching quality why a unique (and not in turn) oil
change was determined.
For this the again developed transmission oil ATF3353 (AO019894503)
makes an additional contribution that we fill in automatic
transmission 722,9 since serienanlauf, with these automatic
transmissions from house. In the transfer case of the 4MATIC-Typen
203/211/220 the oil 001,989 2303 is used, in order to likewise hold
the comfort self-shadows of the 4MATIC-Systems high level with the
Deviating of it a transmission oil changing with the oil FOX ATF 28
(AOO19894603), developed particularly for it, is to be executed
starting from introduction with the transmission 722,8 (Autotronic,
type 169) all 60,000 km.
For vehicles with ASSYST the service position was already taken up to
the maintenance scopes. We will extend the service pages by the note
starting from FIN XXXXXXXXX, are evident starting from WIS update
03,05 the corrected service pages. For vehicles with ASSYST plus is
caused the service position to the service page automatically by the
maintenance computer. The modification of the data records necessary
for it is only possible starting from data record release 09,2005.