Electrical connections only last 10 to 15 years. They are only about 35 to 37% metal to metal contact. That leaves oxygen in the rest of the connection “if” all oxidation and contamination is removed first. If you leave this oxygen in the connection it will, over time (10 to 15 years), penetrate the metal and oxidize the connection, just like aluminum to copper wire. Remove contamination with a de-oxidizer, or by polishing it flat and using electrical grease and a graded bolt for clamping the connection. This will increase the metal to metal contact and remove the oxygen, extending the life of the connection.