Larry,

For what this is worth, my 92 300CE had some problems with the center vent not working. After I tested all the pods and found no leaks the head gasket let go after 150k. Long story short, there was a vacuum hose routed under the battery that had to be replaced. Air works great since then.

Cheers,
Steve

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97 S500 Coupe 139Kmi.
92 300CE 150Kmi. Sold
89 F250 Diesel 220Kmi. Dead
98 GMC 1500 160K.