I'm considering a radical solution to this problem. I'm inquiring about a magnetic in-line filter used in marine applications. It's supposed to treat diesel fuel and get rid of most of its contaminants.

The smallest filter that they sell is a unit that will treat up to 25 gallons per hour for engines under 200 HP. The connectors are 1/4 inch. That seems to be a right fit for a MB diesel. This unit sells for $149 and it's supposed to be maintenance free. I think it's cheaper than removing and reconditioning the tank, fuel lines, etc, or pouring diesel doctor on a regular basis.

I'm waiting for their response. I'll keep everybody posted.