Peter,
I'm Not a tech but i would suggest replacing your thremostat and at least the short hose between the head and your pump. if you have the old plastic thermostat housing i would also suggest replacing that for the aftermarket aluminum one. i remember my neck beaking on mine right after i changed my pump. NOT FUN this means tow truck time! in answer to your other question, I purchased a aftermarket Japanese pump (possibly reman.) 2 years/50,000 miles ago and it works fine so far.
Good Luck, and God Bless America!
Adam

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Current Stable:
01 ML55 AMG
92 500E (a few mods)
87 300E (lots of mods)
00 Chevy 3500HD Diesel Box Truck
68 18' Donzi Marine
06 GT i-Drive7 1.0 Mountain Bike (with GPS!)

PREVIOUSLY OWNED:83 300SD, 87 420SEL, 88 420SEL, 90 420SEL, 86 560SEL, 86 190E 2.3-16V AMG, 94 E320