from memory only the flat part of the arm came off (single nut), behind that was the spring loaded ball bearing which will disappear into the oil in your bilge and take 30 mins to find (you will have oil there as if you're doing this job you have an oil leak from the gearbox).
once the arm is off the seal comes out with no further disassembly needed, I used the sharp tip of a small screw to get it out but this does risk scratching where the seal sits (I was told the trick of running the engine afterwards and verified it when changing one with someone else)
the new seal will be tight to slide in, once I had mine partially in I used the flat part of the arm to seat it fully.
I used a small blob of grease to hold the ball bearing on the end of the spring to reassemble.