To keep things tidy, here's a set of links to Optimum Avengers DVD replacements topics:
Avengers Set 1 (Series 1+2) Replacement Procedures
Avengers Set 1 (Series 1+2) Faults Detailed
Avengers Set 2 (Series 3) - no disc faults
Avengers Set 3 (Series 4) Replacement Procedure
Avengers Sets 4+5 (Series 5+6) Replacement Procedures