vauxhall

I have a 1 zufe 4.0 l v8 with auto overdrive box . I am lost . I loose all the oil and there are no leaks. Top it up and it drives great. Oil is sweet smelling red , changes gears up and down smooth. Engages Drive and reverse nice and smooth kick down while driving smooth so I have no clue what's going on. Once a month I run out of oil and there is not a drop under the car while she parks or under the chassis nothing. Can you help please.

Kind Regards
Allan