This is what I would do.

Buy one of these
http://www.grainger.com/Grainger/SPOTCHECK-Dye-Penetrant-Kit-3WU63

Inspect your old style pump annually/30k miles. Maybe even every 60k miles. If/when cracks start to appear, you will see them before it fails.

EDIT:
Look at the bearings too, obviously

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08 R320 CDI current

Past
95 E420
87 300D Turbo 5spd
90 300TE
83 300SD
85 300TD
92 400E
85 190D