You can check for a restricted cat. with a vacuum gauge. Hook the gauge to manifold vac., bring the revs up to three grand or so and hold the revs steady while watching the gauge. A dropoff in vac. while holding steady revs indicates restricted exhaust, likely the cat.
Don't expect much from two liters dragging 3400# around.
To answer your question. The aftermarket issues are usually fit and lifespan rather than working or not.
If yours is bad then it means it has lasted 15 years before failure. If you need another 15 years of service from it then buy OEM.