[ReneT]

I think too that the the alu idlers turn noisy quite quick.

If you do run aluminium idlers make sure that when you rebuild your gerbox, you put them the same way back in. Keep the one closest to the topshaft at that spot, same with the one closest to the diff. Also keep left and right orientation the same. They wear less like that.

Having said that, I run topshaft-plastic-alu-diff since a while.