If you lost some sele oil (reservior in the engine bay) then you will have some sort of leak in the system and this could be linked to it dropping out of gear. But then again sometimes owners just think the sele oil level is low when it's not.
Couple of things to try - is the sele warning light coming on? You really need to get it on diagnostics to check systems pressure, clutch rod length, etc. Can you hear the sele pump running, especially when you open the drivers door? Could be as simple as the pump relay. Other thing to check is gear oil level - take out the fill plug in the gearbox and see if oil pours out. If so then the actuator is leaking sele fluid into the gearbox. This is bad.