I had my rear window resealed after I painted my 87 T.  Pay the professional to do it just make sure they have a good track record locally.  Swing by the shop and watch a few installs.  The job should be no more than $50-70 dollars.  They should remove all the trim, cut the window out, clean it up, clean the window frame up, put down some type of brushable primer, then re-caulk the frame, install glass, back fill glass with caulk after it is installed, and finally replace all trim.  Also pick up a few extra trim clips as some will probably break or will be missing when the trim comes off.  I went to the junkyard to get the clips and saw some really poor window caulking and installs as I gathered trim clips.  The install should look clean after they put the glass back in.