One option is to replace the 3.5oz with a Palmer Stabiliser;
https://palmer-pursuit.com/ecom/product_info.php/cPath/22_23/products_id/28?osCsid=ad2b5b4cf5f14675fb41fd7d6d858a61
One of the best products around for CO2 and with an anti-syphon will keep liqid out of the marker and make for better consistency.
I just so happen to have one for sale pimp pimp so drop me a line at
olly.bell@btinternet.com if you want to pick one up cheaply
Also if you strip the rear reg/on/off assembly, look at the holes that carry gas from the rear to the front sections and see if they line up when the parts are assembled. If so all good, if not then might need a hole drilling, check out
http://www.automags.org/forums/ or the Mag forum at PBNation for more info and tech advice aplenty.