I have a 85 300SD (220000 miles) I rebuild the vacuum transducer (the blue thing) . It was hissing at me. After I found out a new one would cost nolm$ 125 at dealership ,I tour apart the old one and it had a bad O-ring . I replaced it put back together and seems to be working fine. I notice that the vacuum converter is also hissing (vacuum leak) . The thing the egr line goes to is also hissing like it is looseing vacuum . My Question is. Is it normal for it to make noise or is the hissing from the vacuum converter my problem.