Easily repaired the leaking blanking plug
I had the same issue on my selespeed alfa 147 actuator just this week. I think its yet another Alfa Romeo design flaw on the actuator. It has two blanking plugs either end which I presume is how the internal parts are fitted while being assembled.
With all the vibrations and the movements of the actuators internal pistons etc the 31mm internal cir clips fracture over time and hence the pressure forces the fluid out at the weakest point hence damaging the o-ring. When you run through the gears you can see the blanking plate push against the cir clips. It does all this with no fluid leaking so I am thinking there is a slight tolerance accounted for.
I have a couple of old actuators I use for parts and if you press your finger against the inside of these blanking plugs, you an also see it moving ever so slightly, so it must be on all of them.
I am surprised they didn't think of a better way to secure these plates as cir clips like any hardened steel will fail if repeated vibration and pressure is applied to them, its probably cost.