If you replace it see post 2 above. These units come with different levels of bells and whistles. All of them are three speed reversible fans that are much quieter and move a lot more air than the oem fans. The next step up is a thermostatically controlled fan, which I have for leaving pets in the trailer. The ultimate are fans that automatically shut when it rains and with a remote control so you don't have to walk across your trailer to turn it on. But it's still a camper and people have different ideas of "roughing it".
You should know you will have to do some minor cutting to the ceilng and roof to get the fan to fit. Be careful not to cut into the wiring harness which is also up there. No big deal.
The only reason I see for keeping the original is if you are a vintage airstream purist or don't have the $200 + or - for the aftermarket unit.
Sail on silver girl. Sail on by. Your time has come to shine.