I have seen this type of connection fail after just a few years, but it was an outdoor application exposed to cooling tower drift. The AL had corroded, and pitted away where the CU was in contact. Additionally, the AL oxides swelled in between the connection, forcing the lug away from the pad.
Similar installations at the same plant were inspected, and were found with corrosion and pitting, but not to the extent of the area near a cooling tower.
Hubble makes a NEMA bolt-hole dimensioned metal strip that goes between the lug and pad for this application. It is a thin plate consisting of two sheets (20% CU, and 80% AL by thickness)of the two metals molecularly bonded.