Since OP has fixed the problem, I hope it is okay to ask related questions. I also have a subzero 550. I also had the freezing freezer drain problem, solved differently.
Q1. I can see the front rollers on mine. Are there back rollers? I see a hex head connected to a long rod that goes to the back on each side. I wonder if it raises/lowers rear rollers. The hex head is loose now. Serial number is P1107792.
Q2. I read that the bottom insulation of this old refrigerator is soaked with water by now and remains frozen, which is the root cause of freezer drain problem, and a mullion heater is needed to dry the bottom. Please educate me on this matter if this should be done with the refrigerator off, how many days, etc. When I first turned off the refrigerator, water dripped from the bottom for 2 days.
Congratulations to the OP for solving the problem.