Corrosion Inhibition - Under New Engine Hood

My first new engine, a Tohatsu 302t I sprayed uner the engine cover with Waxoyl which gave super protection and when I came to sell it after 7 years I steam cleaned it and it was immaculate BUT in the meantime picked up dirt and looked awful and was a bit sticky to handle things under the cover. My second engine a Tohatsu 20 4T I sparayed with WD40 and it has not done as well having a fair bit of rust on all the bolt heads and other metal parts and some corrosion on the ali casting lower casing after 7 years use but only 350h hours(sail catamaran).
What is the best spray on corrosion preventative for under an outboard engine cover on an outboard that protects but does not attractive dirt?

Ummm....none. By the way, this is the yamaha forum. So ill suggest to you the same as if you owned a yamaha....does your yamaha owners manual state that you should spray anti-corrosion to the engine or anything else under the cowling? Nada. The reason you're seeing grimm build up is because the spray on is attracting it. Always follow procedures in owners manual...if it says do it, then do it. If it does not say do it...

Actually, Yamaha does recommend that the power plant/power head be sprayed so as to help keep corrosion at bay. They even published a youtube video about it.

https://www.youtube.com/watch?v=S_I9vYz9qVc

I imagine that Tohatsu/Honda would say the same.

From a Yamaha owner's manual:

Thanks for the info - I will get some of this Silicone spray!

Cat Ballou,i also run a 51ft charter cat in Caribbean salt water YAMAHA FT60 four stroke,CRC also makes a similar product with a waxy finish that attracts dirt probably the same thing.I can tell you nothing works like that stuff.Forget the dust on it just do it,you can also clean it down with a paint brush and some deisel oil when you feel like or years later and the motor looks like new.You can't reinvent that wheel with some sewing oil in a can.