Originally Posted by 531Aussie
I can't remember if it's the RX100 or the RSX, but one of them was apparently the exact same mecahanism as the 105, but with a different cover.
That was RX100. RX100 had the same internals for all the components as 105SC except exterior trim and housing was slightly heavier. This is akin to what Shimano did with the Deore DX and Deore XT back in the early 1990s.