It's mud and water, the spring side was fairly full of poop when I got it but I must have not got all of it out! I've had the lowers in the dishwasher this evening, far better! This is the dude with massive wear, hopefully they will last me the summer!
I remember reading about drilling the z1s, and shimming too. I think I chucked away my z1 spares, I'll have a look next time I'm back they are yours if I find them!