I have a 2000 201D. How do I test my fuel gauge to see if it is bad. Right now it is reading full when I turn on the key, I know that I only have about a 1/4 of a tank? If it turns out to be the sending unit, what is the best sending to get and where would I purchase one? I understand that I can access the sending unit from behind the drivers seat? Any issues replacing the sending unit? Thanx in advance for any suggestions regard this matter.