Pace Arrow parking brake

I have a '90 Pace Arrow that the parking brake has stopped working. I am new to RV's but I have been looking at this one and it has something that looks like drum brake around the drive shaft. I have found the pump that should apply the brake fluid to the parking brake and the pump is working. While checking I found the rear master fluid to be low or no fluid. I have looked for someplace to bleed the parking brake line to see if it has air in the line but so far I have not found anyplace to bleed the line. Can anyone out there help me? Thanks
Pace Arrow parking brake

Your question is a bit confusing as you appear to be asking a question about the drum-type of parking brake on an F53 chassis, and then one about the rear brake fluid.

Is your parking brake a drum-type around the driveshaft just behind the transmission? If so, its filled with transmission fluid, not brake fluid. It doesn't, however, share its fluid with the transmission; it has a separate filler plug. This type of parking brake is operated by pressing on the pedal that pulls a cable that pulls on the operating lever at the drum. There is no connection to the service brake lines on this type of parking brake. Its also very difficult to service, other than to ensure it has fluid. If your parking brake is not as I've described, then I'm not familiar with what you do have and how it works.

WRT a rear master cylinder, that implies that you have a tag axle with supplemental braking. I am familiar with FW-installed tags on F53 chassis, but not prior to 1995. On 95+ tags, there is indeed a second master cylinder that operates the tag brakes. The primary service brake system provides pressure to the second master. The two fluids do not mix together. With the drum-type parking brake on the driveshaft, there is no mechanical parking brake on the drive or tag axle. Again, I'm not sure exactly what you have so my info may be totally wrong for you.
Pace Arrow parking brake

The chassis of my Pace Arrow is an Oshkosh. Like I said I don't know how this parking brake works but when you put the shift lever in Park you can hear a pump running and it sets the Parking brake. I don't know if it is set with brake fluid or trans. fluid, but I have not seen an operating lever to the going to the drum that surrounds the drive shaft. Thanks for the input but I think I have a different chassis than the F53 Thanks again