loose rubber roof

While doing a roof inspection I noticed that there is a area around one of the plumbing vents that is not adhered to the osb. It extends about 5 or 6 inches on one side and only a 2 inches on the other. Should I cut the rubber so I can re glue it or is it not big enough to worry about? I guess a third option would be to use something other than rubber cement that I could squirt under the rubber. What would be a good glue if this is the best option?