If the original lasted 20 years, why not get a genuine land rover silencer? Must pay for itself over time compared to aftermarket ones which might last a couple of years. My mid section (tdci) was looking a bit tatty last year so I bought a genuine, delivery miles take-off item (from a chelsea tractor conversion). The old one is still ok and got through 2 more mot's since I bought the replacement which is still on the bench. Old one is now 10 years old and still ok.