Refactoring Event Handlers - How to go about this for growing WinForms application
You can create a Dictionary, where key is a MenuItem, a value us function/delegate that has to be called on click. All 140+ menu items subscribe to the same event hadler and in that event 
handler write something like  

myMenuItemsDictionary[((MenuItem)sender)]()


this is good, in case when you have no parameters to pass to a delegate, in case when you need to pass them, you can go farther:

define a class 

public class MenuItemHandler
{
    delegate MethoddToInvokeOnClick()
    List&lt;object&gt; parametersToPassToDelegate = ..
}


and the instances of this class have in a Value of the dictionary