SLS Question - not a normal leak - perhaps?

Hello Fellows. I have a question on my SLS that I'd like to pose and get some views on, maybe someone else has experienced this.
The SLS system works as expected, except the o/s rear has started to drop, getting lower at different rates over a day or two. Ahh, you say, leaky bag - but if I leave it in extended mode, it does not drop! So could this still be a leaky bag? Or could it be a sticking valve? My only other observation is that the o/s is actually about 2cm lower than the n/s - so I was wondering if the ECU might be trying to continually level out the system (as it does this for a bit when you lock the car and walk away) and maybe in extended mode it does not?
Is it possible to lubricate the valves?
Before I cough up and replace the bags as a start (they probably need it), I thought I would ask if anyone has experienced this?
Thanks for any ideas.

I'd strongly suspect the bag as it is probably opening the leak when in normal height and rolled over. Try spraying soappy water on it and look for bubbles.
Griff

I agree with @Landmark2
I would change the bags as a start and see how that goes. If you have never done them before they are easy. Just remember to disconnect the battery before you start.

+1 for the bag

Thanks guys. Will have a look tomorrow. Not sure how old the bags are, certainly over 3 years as that’s how long I’ve had this ‘04 model. Hoping you are right, I’ll post what I find.

It was indeed the bag. The roll was stressing the fabric of the bag and causing micro leaks, basically the bag has become worn and porous on the fold which closed up when extended.
Thanks all for making the suggestion.