Always amazes me at the lengths some will go to make do, when the solution is so easy. I know laying on your back UNDER a potentially nasty shower is not something I looked forward to, but the fix wasn't as bad as I thought it would be.
1. Call Heartland and have them email you a drawing of your valve locations. Then using that drawing cut an access door/hole in your corplast. I made mine big enough to actually get to everything comfortably. I then went to the hardware store and got a piece of 10 ga aluminum plate (you could probably use something thinner) about 2" bigger than the hole. It is attached with screws to the frame and automotive u-nuts where needed to hold the corplast.
2. If your cable travels in a nice big loop from the handle to the valve then you're lucky. If not disconnect the cable from your black valve and at the handle. Remove the whole cable, inner and outer. Pull your handle out enough that you can spray silicon in the cable and work the cable back and forth till the whole length is lubricated. Re install the cable MAKING SURE that it is in a nice big arch with no kinks or sharp bends, but don't reattach to the black valve yet.
3. Now is the time to determine if the valve is actually leaking. There are 4 bolts that hold the valve together. These bolts should be snug but not TIGHT. If they are overly tight loosen them slightly. There is a rod coming out of the valve that the cable attaches to that actuates the slide. Spray this rod with silicon and work the valve back and forth. When the valve operates easily, then close it fully by hand, and fully drain whatever has accumulated in your line. Run water into your black tank. Put a bucket under your drain. Go drink coffee, or adult beverage for a couple of hours
I put tank chemical in my black tank so I could tell for sure if the water leak was from the black tank.
4. If you have accumulated water in your bucket, you'll have to buy new gate seals for the valve, because I can assure you that if anything is stuck in the valve, the seals will continue to leak regardless of if you remove the plug. After allowing your tank to drain FULLY. Remove the 4 bolts mentioned earlier to separate the valve far enough to remove the old seals and check for obstructions, then re-install the seals per instructions. Replace the 4 bolts and snug them up. Remember they don't need to be really tight.
5. Now reattach your cable. Go to the handle. With the valve fully closed you should have approximately 1/2' of cable sticking out. If not disconnect the cable at the black tank valve, pull out the cable far enough that you can remove just a little bit of the outer cable. I used a 4" right angle grinder. Remember just a little bit at a time. When you have the 1/2" exposed, your done. seal it up.
You should now be able to operate the cable valve with one finger.When you close the valve the 1/2' is the slack you need to be sure the valve closes fully.
6. Attach and seal up your access door.
7. Mark it on your calendar to pull the door, and lubricate the metal rods on the valves with silicon once a year.
No add on accessories required, no leaks, no aggravation, makes me a happy camper.