Park the machine facing down hill or jack and support the back till you no longer see fluid in the gauge. Gently pry out with screwdriver or something suitable. Clean off the sealing surfaces, coat with black RTV/Permatex (why black? It dries quicker) and press back in, gently use a piece of wood or soft mallet if persuasion is required. Let dry and you should be on your way as long as the sight glass is'nt cracked.