If you were replacing fuel return lines, I believe you're looking at the CCV system, not EGR.

I'd go in and replace ALL the elbows and plastic bits that are part of that system. Only a couple of bucks, and as you've discovered, they become hard and brittle with age and like to crack / crumble as soon as you touch them.

It's only oil vapors, won't hurt anything to drive it around like that. It will leave an oily residue under the cover tho.

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'98 E300 turbodiesel