Definitely read over that post, should help your a great deal. Main thing is you need to figure out where the leak is. I found mine by use of a water hose and moving it around up there while I had someone inside watching for water. Once you figure out where, then you can figure out how to fix it the best way.
When you say near the front, is that roof, window, slide out, pop out, what?
I used Sikaflex 227 to solve my leaks but I also had the roof lining out and
found that where those leaks were there was bolts holding the rear section
to the frame and they had rusted to the point they were not doing there
intended job so I replaced them and thus pulled the sections closer together
and with the sikaflex sealing it was perfect.