Product review (5 stars): Buy all your REFRIGERATOR parts from Amazon.
Look for the defrost heater at the bottom of the coils in the freezer.  It has a bulb inside the metal housing, which is hard to see until you unplug metal housing on each end.  If the bulb is black on either end, replace it.  New defrost heater just plugs in at each end; very simple.  Temperature is now 0-5 deg in freezer, and about 38 deg  in frig.  I also installed defrost thermostat, two temperature sensors, and control panel (motherboard) in back of frig, exclusively with amazon parts for a total of $130, which included shipping. Cooling nicely now.  Turns off and on as it should instead of running constantly.  I highly recommend that you watch the PartSelect.com videos on how to repair your particular frig, e.g., just type in your model number, e.g., GSS25JFPD CC.  Frig parts are cheaper from Amazon, with few exceptions.  I am not very handy. You can do all this yourself, with only a few tools.  Watch the PartSelect.com videos first.  Your kitchen & surrounding area will be messy for a while,  unless you order all the parts before you begin, which is what I strongly recommend, i.e., order a defrost thermostat, 2 temperature sensors, control board, and defrost heater all at the same time ($130 for my GE frig).... after they arrive, clean out and defrost your frig. Then repair it.  If you order one part, install it, order another part, install it, et cetera, it may take you three weeks.  That's what I did... three weeks.  But I saved $2000-$2500 by not buying a new frig.