'Reasonably Level' is the recommendation by Dometic. Norcold lists amount of degrees side to side & front to rear.
Reasonably Level is easier to figure.
Do you feel it is out of level when standing, sitting, walking etc.
If YOU feel off level it IS.
And NO.the cooling portion of OLD is NOT the same today. Same process, same concept but tubing is much thinner in cooling unit now then back when.
Off level operation even for 20 minutes can cause damage. Damage which is permanent AND accumulative. Crystals form, attach to inside of tubing, build up and block gravity flow of coolant solution....DEATH