AKA has made a cut-away of the Excalibur. I don't know of any plans to make one of the Viking.
Basically the left tube, looking from the back, contains the LPR. The right tube contains the valve and hammer which is connected to the bolt via the bolt pin. The solenoid switches air from the LPR tube into the hammer cartridge which then drives the hammer and bolt forward opening the valve and pushing the ball into the barrel. After a selected dwell time the solenoid reverses the air into the hammer carridge which pulls the hammer back as well as the bolt. This is very simplified but pretty well covers it.
Use the tool that came with the gun. Remove the air then the bolt and pin. Using the tool slowly unscrew the ram out. Even after the threads are showing keep turning it as you pull it out. Once it's out clean everything normally.
To reassemble use the lube you got with the gun to oil the o-rings. Put the ram back into the tube buy turning it in like the way you removed it. The tolerances are tight so you don't want to just slam it in until the trhreads contact. You'll probably slice an o-ring. Keep screwing it in until it's in all the way, reinstall the bolt and then air it up. Give it some dry fires to work the oil through and then you're good to go.
If you chop an oring the replacement is a size 015.