I have a customer with a Mitsubishi City Multi system in his house. The condensing unit is located about 40' from the house and the piping runs underground. There does not appear to be a sleeve of any type and I can't even see where the pipe comes in. It just appears in the attic from inside the wall.

There's a leak in the system somewhere. We found a leak at an evap and repaired it but it's still leaking elsewhere.

My question is: how likely is piping to develop a leak buried underground with no PVC sleeve? I hate to excavate this guy's yard but we haven't found a leak anywhere else. It was put in about 5 years ago.