92 300D 2.5T - Carbon Sludge in Crossover and Intake

I purchased this vehicle about 18 months ago with 153K. It is not a daily driver. When driven it is on trips of several hundred miles at 75 - 80 mph. I recently had the vacuum shutoff valve go bad at approximately 160K. I decided if I was going to replace the shut off valve I would do a complete glow plug replacement, replace injector nozzles then balance injectors and of course replace the return fuel lines. I purchased evrything threw Mercedes Source and the job has been straight forward.

When I removed the cross over and intake manifold I was surprised to see sludge everywere and up to 1/4"+ thick in some places. When looking into the block I can see globs on the valve stems. I did a 2 can diesel purge about 6 months ago.

Is sludge normal?
Is this amount of sludge normal?
Is there anything that can be done to minimize it?

I thank you in advance for your help

Regards

Bryan

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