I'm probably tech-nitpicking, but you mentioned a manifold leak but inquired about a muffler system and then asked about headers. All different things. That mixed set of terms is likely to bring you confusing answers. The "muffler system" is a collection of pipes and sound-deadeners that is downstream from the "exhaust manifolds". You don't need a new muffler system to fix a manifold leak problem. A "header" is more sophisticated (and expensive!) version of a vanilla exhaust manifold, designed to improve engine performance by streamlining the exhaust gas flow.
As Ex-Calif says, you need to fix the exhaust manifold leak. That could be as simple as needing a new gasket or as bad as a replacement manifold and/or re-machining the cylinder head, but all of those involve a lot of labor hours in addition to parts. Probably more total cost than a '94 Challenger is worth unless you can DIY.
If you choose to replace the stock manifold with a header-type manifold, the labor effort/cost is similar but the header part is probably substantially greater. I doubt if you would realize enough performance benefit to justify it, even though it would be superior.
As you first dive into the world of car modification, you’re tossed into a massive word salad with all sorts of words, terms, and acronyms that you’re supposed to know, but no one really ever takes the time to explain them. When exploring the world of bolt-on modifications, you’ll see these...
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