Loose cylinder head bolt

[onna]

Noticed bike was leaking oil earlier this week. Now trying to tighten up the nut but I'm not having any luck getting the wrench into the area. Pretty sure its a 10mm bolt since it fits on the back one. Thinking the leak is from the bolt being loosened over time and not needing a new gasket. Only a 2007 with 5,800 miles on it and oil change was done last month with replacing the oil filter.