The plate is going to below freezing and you don't want the solution to "freeze" and expand -- that would likely cause a number of problems.

A eutectic solution can be a lot more complicated than a little salt in water...http://www.pcmproducts.net/files/PlusICE%20Range-2013.pdf (I just searched the web)

http://www.asycold.com/images/Explain-Eutectic-Plates.pdf

http://www.refrigeration-engineer.com/forums/showthread.php?14543-Help-with-eutectic-solution-pleasehttp://www.refrigeration-engineer.com/forums/showthread.php?14543-Help-with-eutectic-solution-please

http://www.refrigeration-engineer.com/forums/showthread.php?14543-Help-with-eutectic-solution-please

(Solutions can separate and then you have a number of unintended results)

If you had access (which you may not), then you could probably solder the leaks. My sense is that you might be able to use a sealant, but I'm not sure what will be in the solution.

If it's just potable anitfreeze -- then you would need to have a goop that won't be attacked by the glycol AND that won't get brittle when the plate gets to (say) - 10 degrees in places.