Jez,

Here's how to bleed the damper and chase the air from the cartridge:

1. Pour oil into upper leg allowing oil to settle into the cartridge.
2. Pull the rod and stanchion tube up and down a bit until it is filled about an 100 mm from the top fully compressed.
3. Cycle rod to remove any air bubbles until damping is smooth through out the stroke.
4. Add more oil as per manual [see below].

Measuring the oil level:
- Push down the stanchion
- Pull out the rebound rod
- Measure the distance between the top of the stanchion and the oil
- Deville 140 : 60mm | Deville 160 : 50 mm

The picture below might help:
goo.gl/jrh9RI

 Fantastic, thank you for the reply. I will give this a go and let you know the result. Cheers Jez

 Even after 2 years the seals didn't need replacement so I left the old ones. BOS makes the best seals out there!
I know some guys used the new Fox SKF seals as alternative but I wouldn't go there.
If you're looking for BOS ones you can get them in these stores:
1) www.madelkcycles.com
2) www.surf-sales.com

 i just got my fork back from Bos, had it warrantyed after the air side seal's blow. (had 5bar in fork), they told that normaly those seals/oil need replacement every 1-2 year depending how often i ride. Just wanted to know if in future i need to replace them where can i get some. Anyways thanks for links, and good that you added photos.

 brute force

if nothing helps, use hammer and big flat screwdriver...

 Got them out in the end, bent the screwdriver though!! Just a quick question, the high low rebound knob on the bottom, how does it go back together? Do you tighten the Allen bolt on top and the Allen bolt on the side of the red knob when both knobs are fully closed? Thanks

 Glad you managed to remove the seal without breaking anything, aside form screwdriver

As for the rebound knobs assembly:
[1] You put the red knob first and tighten the small Allen bolt on the side.
[2] Then you put the silver knob and tighten the bolt at the bottom.
[3] It's good to hold the silver knob with some adjustable wrench so it won't turn while tightening the bolt.

See pictures below for better understanding:
[1] www.pinkbike.com/photo/9140988
[2] www.pinkbike.com/photo/9141014
[3] www.pinkbike.com/photo/9141005

 It's good to remove, clean and lube air piston from the left upper leg.
However, you don't need to remove the rod on the bottom.
Please refer to the picture below for basic service and oil change:
www.pinkbike.com/photo/9141036

 BOS Deville 2011 Manual:
www.bosmtb.com/uploads/media/Deville2011EN_01.pdf

BOS uses oil viscosity rated at 15.60 cSt@40C . The closest to this specification is MOTUL Fork Oil Factory Line Very Light 2.5W. I also use it for my Avalanche cartridge.
www.motul.com/system/product_descriptions/technical_data_sheets/2624/original/Fork%20Oil%20Factory%20Line%208219-18-17-16%20%28GB%29.pdf?1303320788

Other recommended oils:
Golden Spectro 85/150 Cartridge Fork Fluid 5wt
Pro Honda HP Fork Oil 5wt
Pro Circuit Fork Fluid PC-01
Yamalube 01 Suspension Oil / KYB 01
Bel-Ray Fork Fluid 5wt

Remember that when choosing the right oil do it based on oil viscosity [cSt@40C] and DO NOT GO BY LABELED OIL WEIGHT, e.g. 2,5W or 7wt. Different oil weights can have same viscosity and the other way around, e.g.
Fox Suspension Fluid 7wt - 31.82 cSt @ 40C
Red Line Suspension Fluid 10wt - 30.40 cSt @ 40C

As for the oil level:
- Push down the stanchion
- Pull out the rebound rod
- Measure the distance between the top of the stanchion and the oil
- Deville 140 : 60mm | Deville 160 : 50 mm
The picture below might help [don't mind the spring]:
goo.gl/rtl1nh

Remember not to over-tight the bolts as they are aluminum and could be easily damaged. You also have to bleed the damper before and chase all the air from the cartridge but I presume you've done it before. And finally, remember to screw the top cap on the cartridge side with the fork fully extended, you might put some pressure into air side to help the fork extend. If you close the cartridge side while the fork is compressed you introduce some vacuum into the fork and it will eat some of the travel and cause inconsistent damping.

One more thing, use some light grease on the dust and oil seals, e.g. Slick Honey or Rock 'n Roll Super Slick. After service the fork should work as new.

Hope it helps.

 Maxima 85/150 5wt is 16.2 cSt@40C. Seems pretty close.