Rear air suspension dilemma

[eckbmw]

Hope anyone on here can advise.
The last 3 mornings my E53 (Air suspension on rear only) has been sitting extremely low and arches almost sitting on tyres.

I have no error message on OBC such as "self lev susp inact" and indeed no errors showing on INPA.

Fortunately I have a copy of INPA on an old laptop.

Each morning I have used INPA to raise the car succesfully and have noticed when hitting key to raise rear end nothing happens, fortunately INPA gives the option of raising both the left and right on their own and this has the desired effect (it's worth noting that at this point I have disabled transport mode).

I thereafter drive the car around town most of the day without any issues but come the next morning there it is again sitting hunched down.

Surely if there was an air leak this would manifest itself quickly and be noticable within a short space of time.

Could it be the linkage on the sensors?