Had the same problem on a '83 p-30 chassis, 454. There is a proportioner valve that feeds the fluid to the two systems. It had sprung a leak. Luckily they could rebuild. They seem to be hard to get. At any rate get it looked at FAST, othererwise...
I have an 83 Winnebago with aluminum roof. It is bare metal and is in great shape after 32 years. Have put eternabond around the seams at the edges and have never had leaks. I'd say aluminum is the best. Don't know why they still don't use it.
