Hi @ssearles ,
Just to eliminate any other problems that may be causing/contributing to what is happening, try running the [https://www.manualslib.com/manual/1259727/Samsung-Rf28hdedbsr.html?page=59#manual|Self-diagnostic function during normal operation] and check for any error codes.
The error code list and meanings are on the next page in the service manual. Do not be confused by the model number of the refrigerator at the top of the pages as the manual is also for your model. - see page 1.
Is the compressor running continually trying to cool the fridge down?
Low refrigerant usually results in cooling problems e.g. freezer/refrigerator too warm not ice build up. Maybe check for any oily residues on the condenser coils and on or under the compressor. There is a special oil mixed in with the refrigerant to lubricate the compressor and if there is a leak then the refrigerant will escape to the air undetected but the oil may leave a trace. Although after all this time if there was a leak the refrigerant should have all been gone by now ;-)
Did the technician measure the low and high side pressures of the sealed system? The pressures will indicate if the amount of refrigerant is correct and also if there are any restrictions in the sealed system. Sometimes a restriction in the system can cause ice build up on the other side of the restriction in the refrigerant flow path.
If parts are required search online for ''RF28HDEDTSR parts'' to get results for suppliers that suit you best.
Hopefully a start.