I just had my '91 300D and my '81 300SD serviced at Amoskeag in Manchester. I was thoroughly impressed by by all of the staff there. First off, Lisa at the front desk is a certified Mercedes Benz Mechanic. It's really nice to call and have someone who knows a glow plug from a butt plug!!! Pat and Brian seem to know all that is to be known about our old diesels and really take the time to explain their recommendations.
I had a block heater installed on my '81 and it required a metric adapter which was backordered into the next century. Pat went into the great Benz graveyard and found me one. They also did the brakes on my '91 at a very reasonable price.
I don't post often, but these guys really deserve it. If you're in southern New Hampshire and need diesel service, these guys have it covered. They are located at 599 Front Street in Manchester and their phone number is (603) 669-7750. Good folks and great service.
CW