If you don´t hear any noises when you move the Z-axis and you don´t have any weird artifacts on the print (like I do), then you´re fine.
In my case the problem is, that the linear bearings where probably not lubricated bevor assembly, so there is no grease inside the Bearings.
Lubricating the roads won´t and didn´t help (I tried it), because the Bearings have sealings to keep dust outside and the grease inside.
When you lubricate the rails, the sealing just pushes the grease up and down while moving.
Mechanikus explained everything in his thread Things to do first with a new J1
I´m waiting for my new syringe tips, so I can try again hitting the ball bearings with grease inside the linear bearings.
Perhaps I can make a small documentation, how I did it with the syringes. Usually you have to disassemble the Bearings from the road and lubricate everything, but I don´t want to mess around with the J1´s housing.