heads not level - thoughts please :-)

[curious aardvark]

nozzleheightdifference.jpg

So does anyone know how to raise the right head ?
Probably only about a half or quarter mil difference. But it means I can't calibrate both nozzles to the same degree.

As I only used it briefly when I got the machine and it got jammed and basically I've been using the left head since then. I have no idea if it came like this. Or if I somehow lowered it by unscrewing it and replacing it. I couldn't calibrate properly from day one. That was mostly the unlevel bed - but this might have also been an issue.
Both heads are fully screwed in and won't go any further. So it's not that.

Either way it's no good as it is.
I did think maybe unscrew the left one a half turn - but the left head has always behaved impeccably, so i don't want to bugger it up.

Help !

My current thought is loosen the right carriage bolt and stick a couple sheets of paper on the right side to level the carriage directly. But that might bugger up the left nozzle, maybe. It'll be tilted - only very very slightly, but still tilted.

Anyone got any better ideas ?