Plastic oiler tubes are the ones that fail - the bottom end blows out. The metal ones, I believe , should never need replacing.

I just replaced the plastic tubes on my E420 as a preventative measure. My friend tried to do the same on his '93 500e at the same time, until we discovered that his engine had the metal tubes (12/92 production date).

While you're in the engine, I'd replace the plastic chain guide at the top of the chain on each side. Takes only a few minutes. Mine was brittle - very brittle. MAke sure you put plastic wrap all around that sucker when you try and remove it - the platic tabs that hold it together will reak and fly off otherwise.

Troy
1995 E420 95k