There have been several OGR threads on replacing (vs. maintaining) the controller using sealed switches. Most popular approach seems to be a center-off DPDT momentary toggle switch as illustrated in this OGR thread. Or the DPDT functionality can be "separated" into two independent momentary pushbuttons like the original controller. I don't recall if anyone has found/identified a modern sealed momentary red pushbutton that drops into the original controller housing if it's important to maintain the original look-and-feel.
As an aside, I recall opening up the lever controller for the MTH UCS fully expecting to find a similar "stacked-leaf" contraption. After all, the controller has that last-century "bakelite" appearance! Imagine my surprise in discovering a modern sealed DPDT momentary switch. 
