Our boat came with a Nova Kool side by side fridge freezer which we really like however my wife noticed it does not cool as well as it first did when we purchased the boat 4 years ago. I kept a close eye on it on our last trip and did notice it had a hard time getting things really cold even on the highest setting of 7. I pulled fridge and inspected visually, no dirt or dust bunnies and the compressor and cooling fan are working well. No obstructions at the ventilation holes and it is not exactly scorching hot nowadays.

So my question is what needs to be checked or looked at to tweak the unit to perform better? I assume checking r134 status is probably the most likely culprit.