I have a 1983 mercedes benz 300d turbo diesel with only 129,000k . i been driving my benz for years and this is the only year with problems. my fuel gauge is messed up. when i turn it on it only goes to half and i have a full tank. is there any kind of conditioner or cleaner or anyway i can fix that. i am now going to check my tank by milage but having a gauge is much better i will appreciate the help.