Freshly updated Ldraw.xml

[Jaco van der Molen]

It should turn 180° over y, so I put transformation ay="1", but it just won't turn.

I think it does what you asked for: rotate around ay by 0° (parameter angle="0")

Hmm, OK. I am not yet into this.
So, if I say ay=1 then the value of angle should be 3.141593.
This is Pi? Why is that?

Edit 2: after much trial and error I think the correct entry in ldraw.xml for this part should be:

<!-- 57999 Train Wheel for RC with Technic axle holder and Rubber ring-->
<Brick ldraw="55423.dat" lego="57999" />
<Transformation ldraw="55423.dat" tx="0" ty="0" tz="-0.65" ax="0" ay="1" az="0" angle="3.141593" />