GP40MC on the Lowell Line - 10/21

I was riding the 315 out of Boston today. I had fallen alseep after we left Boston but awoken after Anderson by the horn. There was a 5 car set with GP40MC #? on the siding. I don't know if that 316 or if they are storing sets there during the day. Anyinfo would be great.

I don't have much to contribute, but what I presume was that set, with 1628-375-373-1608-526-1127, ran as a southbound extra later in the day, passing West Medford about 12:15. I could post a pic but it didn't look any different than any other commuter run.

Maltby Turn out.

Thanks for the info. I was just wondering what it was doing there. I thought they had run out of room at BET to store sets.