Sub-zero 642 refrigerator not cooling intermittently

[eatkins]

I have a 14 year old Sub-zero 642. The freezer works fine and holds temp. The refrigerator section will hold temp for days or weeks no problem and then all of a sudden go from 38 to 45. I thought that maybe it was because we overloaded the fridge but it happens whether full or less full and no matter the temperature in the house. I have no issue calling in a professional to fix it but I want to know a little about the issue so I am not taken advantage of. Any help is appreciated. I have looked at other forums and see others where the same thing has happened but haven't seen a consistent answer. 

Thanks in advance for any insights. 

[AlboGator]

Greetings my frozen Canadian friend. 

Could be a number of things. Do you see an iceball in the back of the refrigerator about middle left? That's a dead giveaway of a sealed system leak. That's a common problem on these. Other than that it could be a cold control, condenser fan, dirty condenser, door switch. . . A number of things. Check to see if your condenser is clean first. Did you notice if the refrigerator was running when it was hovering at 45? And how long does it stay at 45? What are you using to get that measurement?