very basic question but how do I locate a hole in my AC line?

The previous owner had some paperwork from their mechanic mentioning a hole in the AC line which leaked out all the gas. They quoted $600 to repair and refill. Unfortunately the paperwork doesn’t indicate where the hole was located and the shop has since closed.

How can I best locate a hole in the system? I can’t find any info on AC lines or repairing them

2004 X5 4.4i

__________________
Garage:
1997 E36 M3/4/5 Arctic Silver
2004 E53 X5 4.4i Titanium Silver
2006 E60 525i Black
2000 E39 540i Black Sapphire