Sure, but the cost and repair would be more than half the price of a new refrigerator. 21 years is very good, and its exceeded its average life already.
The sealed system consists of the compressor, condenser, evaporator, heat exchanger, filter/drier and refrigerant. Common problems with a sealed system are bad compressors, refrigerant leaks, and system restrictions. Sealed system repair costs will often exceed the machines value.