cxracing downpipe to stock o2 housing leak

[bsbllfit7]

hey everyone i have recently installed a 3inch exhaust system on my car. I have only ran into one problem and that is that there is an exhaust leak on the passenger side bolt on the downpipe connection to the o2 housing. There is not much room in that area to tighten the bolts down. No sockets will fit and the right side wrench is too long and bumps into everything. Im trying to figure out a way to tighten this one bolt enough to lessen or completely remove my exhaust leak. Any help would be awesome. Stock o2 housing by the way,

 

[fwdmaster]

Get a small open end wrench and place it on the bolt and have someone tighten the other end underneath the car, btw is your stock o2 housing ported to match up with your downpipe, if it's not, that could also cause a leak