My 06 F150 - 4x4 - 5.4 - transmission required 3/4 qt.(litre) approx. 600 mi.(1000km.) ago and now is down another approx. 3/4 qt. (lire). Can't see any sign of a leak.
Is there any way the oil can get sucked into the engine or ? via a vent/vaccume line or ?
Will also have to check the transfer case.
What are your thoughts ?
Thanks

 

Check the transfer case

 

Canadian Hunter,
Had my '04 in the shop a couple weeks ago for a routine service at 102K. Trans was 2 qts low, T-case was 2 qts hi. They had to pull the drive shaft to get the t-case out and replace a seal. Grand total was $527 USD. All is well now. By the way, once they pulled the drive shaft, the rear seal started leaking so they refreshed that as well. Good luck!

 

I'm far from a trans expert but I don't believe a vacuum modulator valve has been used on Fords since auto trans became electronic. That would just leave the seal between the trans and transfer case.