The link to the slideout controls is from a switch at the pedal. So a defective brake mechanism does not keep you from moving the slideout.
However, a brake that doesn't hold is a brake that doesn't hold. It would be a good idea to chock the rear wheels any time you park.
There was an earlier version of this mechanism for which repair parts were available, and this may still be the case for other examples used on larger truck and RV chassis (this brake on the driveshaft is pretty common on medium duty trucks with disk brakes all around and no air brakes). But I suspect the cost of removal and taking it apart to rebuild it is not that much lower than replacing it with a new or re-man unit.