Should engine mounts always be installed as a pair?

I thought I was ordering two, but I only got one. The shaking in my car seems to be focused on the right, air filter side. The turbo and air filter vibrate and shake like mad. The air filter mount closest to the side of the car screws up into the air filter housing and is held in with a nut. At idle, it shakes and vibrates so hard, the nut works itself off the screw within ten minutes.

So it seems like I should put a new engine mount on that side of the car. Does that make any sense, or does it need both?

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1983 MB 300SD Turbo Diesel