Thanks - It was actually the first thing that I checked and it looked fine and passed the digital multimeter continuity test.

After much time and head scratching I ultimately removed it and found a practically invisible hairline crack (continuity still checked out OK but obviously the fuse couldn't handle the 10-20 A load from the fan and was the cause of the blower's intermittent operation.

With no dealership nearby, it proved surprisingly difficult to find an exact replacement for the troublesome 30A strip fuse. Had to use a widely available "Cooper Bussman FLD-30 Fusible Link" which required slight modification to narrow its mounting hole distance and decrease its overall length. Also used a utility knife to cut a clearance hole (window) through the top center of the Mercedes strip fuse housing.

In any case it is now fixed and working fine. Total cost out of pocket was $10 for new motor brushes and $4 for the new and better designed fuse.

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One note on the 300E blower motor R&R procedure: if re-installation of the wiper assembly seems tricky, it may be because the top weatherstripping can easily catch under the base of the windshield. Once this weatherstripping is properly seated, the wiper assembly should align properly and mount very easily. Whole job probably should have only taken a couple of hours, but for the first time do-it-yourself mechanic, figure about double that time.