Need repair help for my air pistol. Domino FAS 604

DIY!!! I would over lube everything with Alphabet org Auto trans stop leak quick fix first work it in dripping and all and let sit for a day. Never can tell. Flip the breech barrel o-ring around too. Can't hurt it's leaking anyway. Did it for couple buds guns who didn't want to send their SSPs, multipumpers and Co2s out and pay to repair plus roundtrip shipping and wait time just to get them to shoot again. Talking really Tight PPL!!! In fact it worked in several instances. PCPs soak O-rings only and clean very well with Dawn then silicone oil or divers grease after that before reinstalling don't want petroleum based Alphabet org in high pressure cylinders!!!

Then (after the Alphabet org auto trans stop leak quick fix) of that doesn't help after few days working it in and flipping barrel breech o-ring read this...

http://www.targettalk.org/viewtopic.php?f=4&t=53523&sid=ab75b965a2f2c4b1de2dafff16623f19
 
Decades ago I bought a used 604 that eventually needed to be resealed. Overcoming my fear of the unknown enough to CAREFULLY go into it armed with just common-sense and basic mechanical abilities, I found it very easy to disassemble and reseal with common o-rings

I then used it to tie the national record in NRA Silhouette after mounting a 6X Burris Mini rifle scope, with a 39/40. Wish I still owned that 604!
 
That's an impressive story gasman.......

I do have a good deal of mechanical ability, so that didn't exactly scare me. My problem, if I were to call it that, is that I'm also an electronics guy. I've got some stuff on my bench right now that has to be taken care of. Also, I wasn't sure how 'common' the o-rings would be that need replacing. So, sometimes I don't mind schlepping the job out to someone else. There are only so many hours in a day.

My gun is on it's way to Dave Slade at Airgunwerks, down in Tn. Thank you to spysir for recommending them. Thank you sincerely to everyone that took the time to reply to this thread, you have all been very helpful !
 
The best thing you can do for servicing your FAS ..which i have mentioned numerous times on forums, is to purchase an O ring selection box kit.

These kits come with a range of O ring sizes from about 2mm I/D all the way up to 25mm I/D with approx 10 O rings of each type. There is never a time I cannot find the size I need and so much more cost effective than keep making one off purchases. It also allows experimentation with different fits. I have improved the fits of some of the O rings in an Air Match, finding its stock O rings were not ideally selected for....it was never the most reliable gun but the one i refurbed is now.

Even better choose an X ring kit ....otherwise known as quad seals. Square in section, they offer a broader contact area. Many of the more technical machines in industry have since turned to quad seals.