so, the 1987 shower walls were tile over drywall.. mildew, mould, and other fun.
I have the walls down to the studs and starting to rebuild. The old shower pan looks to the naked eye to be fine, no cracks or significant wear. Should I replace this as long as I'm in there ? or would it be safe to leave the old one ?
I'm nervous about my ability to install a new pan without getting creaking or cracking down the road somewhere..
If it looks good, no cracks, crazing, or discoloration, and cleans up nice, keep it. Otherwise, trash it. Nearly 25-years old, it doesn't owe you anything. The key to creating a solid shower pan/receptor is to put stuff underneath it like deckmud, or something similar so that it is 100%, or close, supported underneath. Or, build a tileable pan.
Important note - I'm not a pro
Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013