To determine the DOM you have to use the serial number on the gun, not the bottle. I doubt the gun is 4 years old...... Just the bottle. Furthermore, BSA doesn't make the bottles. They are outsourced. The age of the bottle does not reflect any issues in this case.
One of the big contributors to the difference in price is the Mk2 does not have an over-price Minnelli walnut stock with the rose wood, or Palisander wood inserts that accent the fore end and the base of the pistol grip as well as the precise laser cut chequered panels.
Also the regulator. The Mk2 is less efficient than the SE. No specific details other than BSA claims the SE is 11% more efficient than the Mk2.
And the CCS or Customer Configurable Shroud.
I sent an email with my guns' serial number to BSA inquiring as to how to decipher it. It's my understanding through the UK's BSA forums it may take a day or two for a response. I'll update here as soon as I hear back.
Ok gun filled to 3000 and I unscrewed the tank off and will reinstall in ten hrs....at least like Dave said find out where its leaking .
Make sure you remove the bottle correctly. If you dont you will cause another leak by ruining the o-ring on the bottle. You have to loosen the bottle about 3/4 turn then shoot the air out of the regulator. Once the air is out of the regulator you can unscrew the bottle completely. If the reg doesnt empty within 6 - 10 shots unscrew the bottle a little more and repeat the shooting until the reg is completely empty.
Thats a strange comment my MK 2 most definitely has the minnelli Walnut stock along with the Rose Wood Caps as does my spare stock. They must send them to the states differently configured than the U.K.