That is a strange one Mike, I was to believe they did all the maintenance for them at Area 51! but saying that it does seem they do go to Delta TechOps in Atlanta!
Janet 737’s are also said to be serviced at Paine Field in Everett, Washington.
Apparently? in 1994 a Janet 747 was seen arriving at Boscombe Down in Wiltshire..
Much thanks
Mark