Pix is not a model name but a trade mark of the house in its own right. Originally it stood for push-button pencils; because the name Meisterstück could not be registered as a trade mark in every country, Pix was later applied to fountain pens and ballpoints as well. A pen stamped Pix beneath the clip is therefore not a model of that name but an ordinary Meisterstück. Conversely, the absence of that stamping on a modern pen is a warning sign.
The cap top is screwed in place on current Meisterstück pens too, and that same screw also secures the clip to the cap. It is no longer accessible, however, because a plastic cover sits in front of it; only on older Meisterstück pens can the star top be unscrewed. So if the cap top will not come loose, nothing is broken, and force will only damage the cap and the clip. For a basic clean, dismantling is unnecessary in any case: a piston filler is flushed by drawing in clear, lukewarm water and expelling it again, over and over, until it stays clean.