Would normal operating temperature not be sufficient? Isn't this the temperature at which the vehicle will normally be operating? Drive around for 30 minutes and park on even surface at idle check fluid. This worked fine for me - truck shifts great.

Don't you think you are over analyzing this? The engineers at MB would certainly be satisfied by you checking the trans fluid at normal operating temperature unless of course you intend to drive in an extreme environment. ;-)

Also, suggest you change the trans fluid from old fluid type to new type p/n 011-989-45-03-13 (ATF 3353) and change filter. Since doing this my truck 00' 320, shifts more smoothly and predictably. NOTE: Once you goto this new fluid type you can't go back to old type.

Good luck!