Waxoyl brilliant stuff, I always keep a jam jar full ready to seal the odd rust spot. Works a treat on sump plugs...
I coated all my metal brake and fuel pipes from new. All still perfect.
I coat the rear of the wheel cylinders, when I replaced one a couple of years ago it came apart easily.
Watch you don't get the waxoyl on rubber based items, tyres, brake pipes, it seems to swell the rubber, not sure if this is harmful, but seems ok when dried ! Also keep it off the brake discs and exhaust.
If you use waxoyl under the bonnet, it does tend to run out when the engine gets hot especially in the summer.
If you want to wipe waxoyl off, just use white spirit (turps sustititute)
Also good for electrical connections, plugs sockets, rear light clusters.
If you use it in the wheel arches, be prepared to re-coat every year I guess, as it is a high wash area. (5 minute job)
Don't block the drain holes with it though otherwise you will create more problems.
I even used it on the rear suspension joints on the anti-roll bar that used to squeek like anything in the summer, cured that problem straight away.