This does sound as if it's weak. However, a fully charged battery will not show a voltage as high as one that is down. If the battery stays charged, I'd say you're okay. Keep an eye on it. Is this a high mileage alternator? If so, it may voltage regulator/brush assembly time.
If you resort to a new alternator, you will be money ahead in the long run to have a Bosch certified rebuilt one. I've tried all kinds, and these are the only ones that will last a long time.
'84 Euro 240D, 523K miles
'88 300E 5 Speed
'81 300D Daughter's Car
Over 800,000 miles in