Here's a list that I know of, can't vouch for personally, but are possibilites worth looking into.
1. Musica and Arts - Laurel, MD
Don't know anything about their repair reputation. Less than 5 miles from Burtonsville
Recommended by others on SOTW
2. Lee Lachman - College Park, MD
~10-15 miles from Burtonsville
3. L & L Music - Gaithersburg, MD
~25 miles from Burtonsville
4. Washington Music Center (Chuck Levin's) - Wheaton, MD
Chuck's is really not that far from Burtonsville. Can't be much more than 10 or so miles. Course in that area, depending on traffic, or anywhere around DC for that matter, that could be anywhere from 20-40 minutes.
5. Rosso Music Center - Baltimore, MD
The music director for the Baltimore Ravens marching band owns this shop. So, they also do all the repairs on the instruments for the the band. Go figure, but still probably do good work so I wouldn't write them off. The Music and Arts store in Severna Park, MD sends their repairs out to Rosso's. About a 45 minute drive from Burtonsville.
Have to do a Google for exact location and contact info. Hope that's some help.
Cheers!