I've still not uncovered much additional information about the McCluskeys in Durham. (My ggg grandfather was a Patrick Cluskey, whose daughter Margaret McCluskey O'Grady was my gg grandmother.) I have been muddling along trying to find Patrick on census information. The town names that have been surfacing are Darlington, Thornley, and Bishop Auckland.
The O'Grady side appears to have immigrated to Durham from Co. Kerry, Ireland, but I'm unsure of the McCluskeys. I feel there must be a connection with your McCluskey's back there somewhere!