TX200 Maintenance

Well the tx200 may be one of the easiest and quickest springer type rifles that I have to break down. I take out the 4 stock screws. Then take out the bolt that the front trigger guard screw goes into while holding a little down pressure on the barrel end with the back end of the action against a table top. That bolt that the trigger guard screw goes into has loosened on my rifle before so I Loctite it with the other stock screws.
during reassembly.
Edit: sorry didn't answer your question about when? That rifle is so easy to break down I would do it anytime to get to know your rifle a little better?

here is a service video and a link to seal.

https://www.youtube.com/watch?v=fg2U78vl67I

http://www.pyramydair.com/s/a/Air_Arms_Piston_Seal_Fits_TX200_Pro_Sport_Air_Rifles/4083

 
I have a ProSport. It's the same internals. My answer would be when you take it out of the box. Right before you mount a scope. Everyone talks about these rifles shooting like they are tuned right out of the box. I don't agree with that at all. Mine shot fine but had a lot of buzz. So after a couple hundred shots, I disassembled it and lubed the spring to dampen the buzz. This made it nearly tolerable but still not like my R1's. So after about 1000 shots. I ditched the factory internals and installed the Vortek kit with their seal. This is the way the gun should shoot. Now it's perfect. I am not getting the velocities they posted, but I am in the mid 800's, which kills paper just fine. They are great guns but they can be greatly improved.
 
Springers don't need much maintenance. In fact, too much lube should be avoided. Seals also last a very long time.

The main reason to dig into a springer is to improve the shot cycle and get the shooting characteristics more too your liking. Or if you notice a big change in velocity, which likely reflects a broken spring. 

A Vortek or JM kit will improve your TX. Once you get it installed, you should be good for at least 10,000 shots. I have at least 20,000 shots on the Vortek kit in my pro sport.

Good luck
R