Well, the private shop guy is probably somewhat right. The lines usually do run together at some point, and on a 91 that has spent it’s life in the salt chances are they are rusted as shit.
Joe’s answer is your best bet. Find exactly where the leak is, hope there is enough good non-rusted line to cut the leak out, flare both ends where you cuy it and stick a replacement piece of line in there.
I had to do this on my old Fiero and ended up replacing both front lines because by the time I got the leaking one seperated from the good one, they were both leaking. If you take this to a shop be prepared for them to hit you with a big bill if they don’t take their time and cause all your lines to start leaking.