Part of me knew that I should have removed the AC unit then and replaced the seal, but I thought of a lazier way. I used a very liquidy roof sealant. I poured the sealant around the AC unit and let it flow until it found the leak. It worked. It stopped the leak, but I also blocked the drains meant to whisk rain water away from the AC unit. I didn't know this for several months though.
Cut to a few months later and it's getting hot in Illinois. I start running the AC a lot. It's fine for a while, but to my surprise, water starts running down onto the bed. It must be condensation from the AC. This is a problem. the condensation finds a different path each time. Once it fell directly from the AC unit onto the center of the bed. Other times it would slowly ooze out the side, get caught by the top side of my new ceiling and run past a 110volt outlet I installed for my TV and XBOX! It even found a way to drip down onto my wall-mounted TV. Lucky for me the TV and XBOX remain undamaged, but this is clearly a problem that needs a permanent solution.
I knew it was going to be a lot of work. Lucky for me I'm camped out about two miles from my parents house, who have a garage full of tools and equipment that will make it project a lot easier. First and most importantly is space. My campsite is alongside a friend's house, I can just barely fit the RV through the gate and the rear bumper kisses the edge of her deck.
This is a close up of one of the bolts holding the unit one. This was taken after the gasket was replaced. The original had shrunk to about 1/4 of the new gasket's thickness. Removing the unit was actually the easy part, sort of. Since I had used that sealant, I had to use a floor jack and a long 2x4 to press up on the AC unit to break that seal. Once it was broken, the unit lifted right off (but it was still heavy).
With the unit removed, you can see the aftermath of my lazy attempt to seal the leak. Let this be a warning, don't be lazy, you'll only end up doing more work in the long run. I scraped, sanded and scrubbed with various solvents for about three hours.
I started with a putty knife and pried as much of this crud off as I could. It wasn't going very fast so I upgraded to a power dil with a sanding disk.
Once the majority of it was removed, I used Acetone and scrubbing pads to get it perfectly clean.
I'm sorry I don't have more pictures of the cleaning process. Here's the unit on it's side in the garage. As you can see the gasket has been removed. Like the roof I had to scrub with acetone to get all traces of the old gasket off. I also opened the unit and removed dead leaves and twits. Then, just because, I coated the rusty pieces with Rust Converter and give it a quick spot-painting. Notice the clean and clear condensation holes.
That's it! The whole process took me about six hours. If I didn't need to clean up my mess, I think I could have accomplished the whole thing in about two hours.