We are re-building the concrete shower pan over a concrete slab in our 48 year old house. We have gotten conflicting advice about whether to replace the old, cast iron shower p-trap or not. Is it likely that the p-trap could fail condsidering the age of the home (48 years)? In order to replace it, we will have to jackhammer the concrete slab. What is the life-span of castiron plumbing parts. Any help is much appreciated!