It's better to use the clear waxoil, rather than the black stuff - that way you can see where any rust problems are starting, and treat them before it gets bad.
Waxoil is good at what it does, but it's no good spraying it over rust! The waxoil will seal the rust alright, but it also trap the existing moisture (doesn't need much - there is enough moisture in the air) and oxygen (rust is an OXIDE remember - this oxygen can be scavanged from existing rust / ferrous oxide III) and the rust will still grow and spread - though at a slightly slower pace. Clean up all rust before spraying waxoil over it
The use of motor oil is a good idea, it does help the waxoil to flow better, protects for longer (stops it drying out so quick) and will slowly creep into the tiny area that are easily missed by the waxoil. The engine oil does a good job on the front subframe, might as well use it on the rest of the car.
For thinning waxoil I normally just use white spirit, which evaporates fairly quickly ( few days to a coupe of weeks depending on temp) and helps get the waxoil into the small gaps between welded sections, and gives a much better coverage. I usually do one coat, wait a week or two for it to dry, then give it another coat to build up the depth.
Best yo re-apply it once every few years to make sure all the stone chips and scuffs are covered and sealed.
SS
