1. I started using it very sparingly back in February I believe, just on shock mount and CA points. I noticed how new the material made the surfaces appear, so I went ahead and sprayed more on other areas around the axles, dif covers and so on. I pressure washed the underside to remove all the dirt and grime I could and on about May 1st I applied a full can to the underside, everything but the exhaust, and brakes of course. Took that Jeep to the beach for about 12 days, ran deep sand, wet sand, salty sand everyday. All added up probably 250 miles of beach running. about a thousand miles of road. All I had to do to remove the sand from the material was a garden hose and just rinsed it clean. The underside looks better than it has in a year and after that rough month the film is still there (not as much but still there) This material also has a good creep characteristic, it levels itself out after a day or two.
2. The exhaust, brake disks and pads are things I would not spray with it.
3. Hinge pins, High lift jack mechanisms, and on and on. It is lanolin based and does not hurt rubber. You can spray the inside of your bumpers, wheel wells, makes cleaning off mud and dirt much easier.
Fabulous stuff.