If anyone is looking for a replacement for their missing or non working brake reservoir float switch and cap, the one from an Elise may work as a substitute. The Elise cap and switch seems to have the same threads as the universal Girling small reservoir cap. I tried the Girling cap on both the Elise and the S2 stock brake reservoir, it fit on both just fine. Picture shows the Girling cap on the Elise with the stock Elise cap.
Sorry, put this in the wrong forum.