From Dometic:
To enure proper leveling, the vehicle needs to be leveled so it is comfortable to live in.
When the vehicle is moving, leveling is not critical as the rolling and pitching movement of the vehicle will pass to either side of level, keeping the refrigerant from accumulating in the piping.
From Norcold:
Leveling:
CAUTION:
The refrigerator is made to operate within 3° off level side-to-side and 6° off level front-to-back (as looking at the front of the refrigerator). Operating it at more than these limits can cause damage to the cooling system and create a risk of personal injury or property damage. Make sure the vehicle is level before you operate the refrigerator.
Operation during travel:
While the refrigerator should be level when the vehicle is stopped, performance during travel is not usually effected.
Funny.....Dometic statement is very generic while Norcold is more specific and yet Norcolds seem to have more problems.
Just remember......damage from off level operation is accumulative.