Have a 17 year old

Question

Have a 17 year old Kelvinator N640T side by side no frost fridge freezer. Runs well except ice builds up on the bottom of the freezer compartment and when it builds up too much some melts spilling water onto the floor of the kitchen. Were advised that it could be the door seals (have now replaced them with new ones)but problem is still there except that the ice does not now build up as quickly as before. Were also advised that it could be the defrost mechanism. Any comments welcomed. Thank you.