I've just changed the 7 o rings on my 162ei.
As above, there are 2 on the barrel, 1 on the pellet probe, 1 on the front cover of the reg body, 1 on the main reg body that threads into the block ( I had to machine a tool in my lathe to remove the reg body), there's 1 on the reg, and finally 1 on the transfer port. Once the reg body is removed, its quite easy to change the 'o' rings, just make sure the trigger bar is in the correct position.
Peter