BBOB< I don't believe the '79 300 w123 has a monovalve.

Propably referring to the climate control servo.

123 driver, mail it back to chrysler who ade it in the first place!

Fix it soon because it may indicate a siezure inside and may cause over heating, my 2 cents anyhow.

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1979 300D 220 K miles
1995 C280 109 K miles
1992 Cadillac Eldorado Touring Coupe 57K miles SOLD
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1979 240D 140Kmiles (bought for parents) *SOLD.
SAN FRANCISCO/(*San Diego)
1989 300SE 148 K miles *SOLD