URO = U Replace Often.

Although I've heard a rumor that MB themselves were going to URO to source some parts. This is an unsubstantiated allegedly true peice of information.

Electronic parts are generally reliable over many years however if the components are made from substandard materials then you are in for pot luck. The problem with relay units such as the OVP and fuel relays is that the soldering joints are becoming oxidised or separating because of the poor quality solder or original soldering technique.