Rcarter,
if the plastic keeps melting around the post i would most definatly check the connections where the cables connect, if they are not clean that can cause heat from high amp draw.
Also get an amp meter and check the amp draw on the motor.
Check the battery settings and make sure they are set correctly, if it is drawing the battery down too low it can cause a high amp condition and make the controller posts heat up melting the controller cover around the posts.
Also make sure it is the correct battery for the lift according to the battery specs for the lift.
Get a battery company to check the battery out and make sure it is ok, if it is running down too quickly or making too much heat there may be an issue with it.