Every roller coaster in the world has a recommended minimum temperature to run at. I believe Stealth's is around 5 degrees C. However this is only a recommendation from the manufacturers and isn't a strict rule. The problems that occur in regards to oil temperature are not a consistent problem, it is more of a regular occurrence that the oil tends to raise above the line.
I believe Stealth's average normal Oil temp is around 44 degrees C, and the 120 second interval only begins when the temperature reaches 48 degrees C, with a 52 degree C cut off point whereby the ride will be forced to shut down.
Unfortunately it's not a design floor that these problem occur in hot weather, any type of steel, or metal for that matter, expands in hot weather. This is why the brakes getting stuck issue occurs. Unlike other launched coasters around the world, Stealth is not sprayed between launches and relies completely on the lubricant used. Eventually, the lubricant dries out due to the heat meaning the brakes more liable to sticking, as well as this the expansion from the heat causes more friction which also in turn makes them stick with or without lubrication.
The brakes sticking is not a massive problem, and I'm sure even though they have extra help in other parks via nozzles, they may still encounter similar problems.