I have seen a couple common problems. Most common is algae growing and dying in the fuel tank. There is a screen with large holes at the exit from the tank. This coats and plugs with the gunk. Had two just this week.

We take the tanks out and steam clean them.

The other common problem on high mileage motors is in the fuel feed pump. I have never seen the pump itself fail at any mileage, but there are plastic check valves in the inlet and exhaust of the pump that do fail causing the pump to just push the fuel back and forth. The pump itself is mounted to the injection pump on the fender side close to the front. The fuel line from the inline filter attaches to the feed pump. The other side goes to the larger oil filter looking filter. To get to the check valves, take the fuel lines off the pump and keep removing the fittings the fuel line attaches to. The bottom one is 22mm if I recall and the check valves are underneath.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician