My 2010 plus 4 with the MT-75 gearbox has alloy crush washers, they tend to stick to the gearbox and look as though they are the gearbox surface but you can flick them off easily enough! They don't use copper as it could erode the face surface of the gearbox causing a leak down the line (reactivity series of metals scale). I have reused my alloy crush washers several times with no problems.
Yes, disimilar metals create a corrosion cell. Copper and aluminium is a particular watchpoint.
