Tigerfox, you may have heard a misinterpretation of policy where the drier is changed when the system is breeched and has more than 5 years on it. Breeched - meaning outside air has had a chance to enter the system... not a leaky system that has maintained positive pressure at all points.
Some poeple don't change the drier if the system has less than 5 years service and it's open only for a short while during repair. This isn't a hard and fast rule, and some people may frown on this practise, saying you MUST change the drier anytime the system is breeched.
NEVER change a drier on a properly working a/c system simply for maintenance. It is a closed and sealed system.
95 E320 Cabriolet, 131K