I have a 99 Gulfstream Yellowstone C-Class and have just discovered a leak in the cab over area. The headliner material that runs from over the drivers door, around the front above the windshield, and over the passenger door is very stained from previous leaks. I revomed the headliner and the very thin ply that it was attached to to try and find the leak. Today it has rained very heavily and it's dry as it can be. I believe it only is leaking when driving in the rain, or when i wash the unit and force water in and around the seal. How bad is this? Can it be repaired from the inside where the black, rubbery, shiny material can be seen, or it something really bad? So far the only damage I can find is the stain on the head liner. All the wood I have inspected still looks ok. Nervously awaiting your replies.

Just my 2 cents: Take the coach for a ride, especially at freeway speeds, the next time it's raining and see for yourself where the water is coming in. This will save you a lot of work and worry.

Thanks troth.. good idea. also may use the garden hose.

By the way... I called GulfStream 2 days ago and no return call yet.

I have a 99 yellowstone that had a leak when I purchased it but I didn't know this, it ended up being the molding going along the side where the rubber roof connects to the sides under that rubber incert, they had drilled holes for screws but didn't put them in so I had to that all those screwsw out one at a time and put new ones in with a caulk made for the rubber roof. I hope this helps you. Good luck

I would not repair from the inside. Based on your OP, an external force of water must be applied to make the RV leak. To me, this means the leak must be repaired from the outside. Running lights are infamous for this kind of leak. Once you find the general area of the leak, disassemble everything and clean all old calk right down to the finish of the RV.
Re-calk with the appropriate calk and reassemble the parts. Do not calk over old calk. This is true especially in your situation, where a force of water is required to make the leak happen. It's amazing how water will penetrate layers of calk, when force is applied. This is not fun and it is a PITA, but it's the only way to solve the problem.

If you don't fix the leak you will end up with a cab section like ours was when we bought it (deck and front framing rotted). Ours had leaked at the front window in the cab over, the marker lights (replaced and sealed with a white elastometric roofing sealant... DO NOT USE SILICONE) and the metal corner strip also leaked in the past (removed while repairing cab over... replaced butyl tape, new screws, sealed edges with elastometric caulk). We also had a screw (factory installed) that had punctured the roof. This had leaked for years. We found it while removing the cabinet.

Check for your leak or leaks around the windows, marker lights and the seal seperating the roof structure from the front overhead cab.
Also check the window drain or weep holes. They do get dirt in them and prevent the water from draining out. When the track fills up it will over flow and run inside the unit.

If your framing is metal you are in better shape. Spray the framing that was wet with WD40 to prevent future corrosion. If you have wood framing up there you will have to be concerned with rot (wet or dry). My personal feeling is that most C's are prone to this problem because of the extra bouncing they get on rough roads. They used to make supports for the slide in campers on trucks and I think that would be a good idea on most Class Cs. It can be repaired. Good Luck