Mike:

Drain the water from the block and radiator and refill with a mix of Shout! (from local grocer) and water. The Shout is an excellent de-greaser and doesn't foam -- works quite well and run it thru for a few minutes, then drain, then repeat with plain water and drain again. Use MB coolant as MikeV recommended -- might as well since you've come this far.

Make sure you fill entire block by removing the 14mm bolt next to the oil dipstick (there's 2 of them side by side -- I use the one closest to cabin). When coolant starts to overflow from this hole, screw bolt back in and finish filling radiator.

Good luck and nice work!

~Paul

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'91 300E, 206k miles