The repair may have been done with the original gasket. Make sure you ask for the improved gasket that was phased into service in the late 90's. It has a steel reinforcement within the gasket, but even this will not prevent future failures. The gasket reinforcement plate from Hughes that Thaxton linked to is the best long-term solution with the stock intake manifold. Notice, I said "stock" intake. Use of the Mopar Performance M1 intake eliminates that pathetic design flaw (a real money-maker for Mopar service depts). But with the M1, you need to do other performance-oriented stuff. Don't get me started.
First of all, check the intake this way. Get a flashlight, climb up, open the throttle blades fully, and look at the inside of the intake. Does it look oily on the intake floor? If so, the gasket is shot. As mentioned, '96 and newer Magnums have no EGR, but it didn't hide that gasket failure too well. Anyway, the intake gasket is the biggie. Magnums have no knock sensors (funny, my '89 318 Shelby Dakota did....the plot thickens), so there are no provisions in the programming to automatically adjust the timing when pinging happens. While you're in there, put in a new 180 degree thermostat. Unless you have one of those fuel line dis-connecter thingies, it's gonna be a P.I.T.A. to work on the intake still attached to the truck via fuel line. I don't envy you the weekend "fun" you're gonna have.