Vacuum Hoses
Sorry, I was just teasing you and didn't mean any harm. Please forgive me. As I have 4 different vehicles I keep about 10 feet of every size in stock so I'll always have it on hand. As my cars are all 1982 and earlier I keep 3/16". 1/4", 5/16", and 3/8". Your C4 is metric but American sizes of hose will usually work. Vacuum hoses are very inexpensive so I'd suggest buying 10 feet of each size. As every model of C4 is slightly different they all use different lengths of vacuum hoses so it's best to have extra.