Little movement on Z-Axis

Here I’m again, always with problems, hehehe.

The video of my problem:

And the explanation: There is a little of movement on my Z-Axis. Is there any way to reduce this imprecision? I’m trying to engrave very thin works 0.1mm and this movement of the tool is really annoying because some times it cut on lower position, and some times on the upper (not measured perfectly but this is more than 0.2mm). Is really complicated to fix the zero Z coordinate with this clearance.

Also I would like to ask about any link to a topic or recommendation about maintenance of the Nomad? I mean, should I grease in some way any parts of the Nomad? should I take special care on cleaning often any part of the machine?

Thanks in advance,