I recently removed an old heating element from a pot, that was much older than you are dealing with..probably 10 years. I wasn't able to get it to budge with all my might on the element wrench
. I used a hammer on the element wrench to tap at the outside of the threads for a while, which may of may not have helped. Eventually I used a propane torch on the coupling it was threaded into to make the threads expand a bit , which did the trick.