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the correct rear shock for your base model Deville
is a Monroe 40046 -

the Concours model has ACTIVE/electronic suspension -
the Monroe 40018 is the correct unit -

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the mounting is the same - and uses the same air line connection -
however - your car has no way to control the variable valving inside the shock -
can you install it on your car?
YES - it will fit - and you could bolt it on -
will it function properly?
YES - and NO -
the air-shock part should function properly -
the internal valving will not function at all -
I don't have any idea whether the internal valving stays in the last position it was in -
or defaults the a "soft" ride - or a "firm" ride - or somewhere in the middle -