Are some Admiral fridge parts obsolete?

I have an 10 yr. old Admiral side by side fridge. Auto defrost/freezer drain got clogged, leaked on floor. Repairman thawed it, blew it out and it worked for two weeks, malfunctioned again. Repairman said it needed new (inexpensive) part, but he checked and part is no longer available. Are some Admiral parts obsolete? Does this sound right or should I get second opinion? Otherwise I guess I’m replacing fridge.