Hi Michael,
Hard to tell exactly what the goo is from the pic.
If the freezer is still functional you can repair the insulation with a can of 'Polyurethane Expanding Foam' from your local hardware store (search web).
Clean up the 'goo' first, with gloves on, try:
* to physically remove as much as possible with plastic tools so as not to damage the freezer
* then try cleaning with Metholated Spirits
* If still residue, then clean with Acetone
* dry completely
* apply tape to cover the hole
* carefully make a small hole in the tape the size of the foam applicator tube.
* then spray expanding foam into hole via the tube on the can
* you can put more tape over the small hole for a neater finish as it expands and dries
If you haven't used expanding foam before, try it on a similar sized hole in a cardboard box or other rubbish, to gauge how much you need. It has a unique behaviour and expands/grows very rapidly. Follow the instructions on the can carefully.
Regards
Chris