Various comments on this:
This oil-spray rustproofing won't completely stop the rusting on a rusted car. It will slow it down by at least 90%. So it's never too late. I wouldn't bother having it done on a new car until the underbody has lots of surface rust or you get the first signs of rust in the bottoms of the doors.
Krown used to have a place in Vancouver, but it's not available anymore. Now the closest place with this type of treatment is a Ziebart outlet on the North Shore. Cars that have this done drip oil for days or weeks. I understand this has come to the attention of regulators as a pollution issue, and has been behind the banning of this process in some jurisdictions. This should be balanced against the environmental cost of premature replacement of cars. Not to mention what we have to do to make the money to buy replacement cars.
Knowing that the car will drip for a while, you may not want to park it on a fancy driveway or in your garage without a drop cloth under it.
The oil mixture affects rubber. If it gets on door weatherstripping, for instance, the rubber will swell. I assume this also happens on underbody components like suspension and steering bushings. Oddly, my experience has been that this keeps them tight and extends their lifespan. It also acts somewhat as a chassis lube.
If the spray gets on the rubber or fuzz side window wipers inside the tops of the doors, your side windows will get streaked with the stuff for months. It's not designed to be easy to remove. I have no idea about the effect of the stuff on other components, such as door speakers.
It is difficult to identify all the vulnerable nooks and crannies on any particular vehicle and ensure the applicators treat those areas. I had a '79 Impala station wagon, and they never seemed to get inside the body cavities to the sides of the tailgate. I have a '91 Pathfinder, and they need specific directions to spray inside the back ends of the rocker panels, which are a rust breeding spot on those cars. There were places on both these vehicles that the treatment, and any other, simply would not stop rust. Such as along the top of the windshield.
The stuff makes one "H" of a mess on the underbody and in the engine compartment. Mechanics hate working with the mess that results. You will get false reports that your vehicle has all sorts of fluid leaks that must be fixed. Even false battery leak reports. If you drive on dirt roads, it will cake up with sand etc. making an even more delightful mess. Heavy dust also absorbs the oil off the metal and so degrades the protection.
You can have a partial job done if you request it. For instance, underside only and not inside the doors. I found that having this done every 2 years was sufficient. It would depend on your driving environment and your car. Our '90 Dodge Spirit has almost zero rust, and has never been sprayed. The Impala and Pathfinder rusted enthusiastically, but both were driven extensively outside the city in winter.
The outside of your vehicle may need a very thorough cleaning after being treated. But you should wait for a few days to allow the oil to creep everywhere, or you could be washing it away from places it needs to protect.
I haven't watched it being applied, but I can imagine the quality of the application would vary widely.
All of this has to be balanced against the cost to replace cars, and the resale value.
