So, it has been over a decade and the E53 has done 75k miles since my torque converter grenaded and made a refurb of the trans necessary. It was working perfectly since then with two drain and fills done.

About two weeks ago it went in to fail safe mode. It reverses fine and seems to have drive in failsafe but none in 1st/2nd (?) There was plenty of fluid in it, I recovered what came out when I had a look in the pan. The pan has some fuzz on the magnets but nothing out of the ordinary. When I restart the engine it feels like it wants to move but then reverts to failsafe within the first half second.

I am planning in my head how to get the trans out in order to have a look at the internals. Could be an O-ring, an axial needle bearing or some other mechanical problem I guess.

My question is, could this be a problem in the valve body and if so, what am I looking for? The fact that it wants move before going in to failsafe makes me think there is pressure from the VB in first gear and I would be inclined to assume the VB is ok but any insights would be helpful. (Here's hoping RRPhil pitches in as well :-)

It would of course be less work to just pull off the VB but I have sort of resigned myself to the need to pull the trans. Since the E53 is not critical to our needs I can take my time. However, I don't want it blocking my garage while figuring out what's wrong, it would help to have some idea.....

__________________
2003 4.4i black ext./black int./black headliner (kid's runabout)
2014 535d X-drive, M package, silver/black interior

Sold but not forgotten:
2009 E70 35d, black ext./black int./black headliner (sold 2021)
2006 4.8iS Le Mans blue/cream int./black headliner, SOLD in 2012 sadly...

Other hardware:
2015 Cayenne S (wife's new DD and definitely wroooommmmm)
2016 Tundra 1794 edition crew cab, luxo hauler
2005 Tundra crew cab, weekend hauler. Sold after 150k very happy miles.