I have used Waxoyl for years on my Landy. Works a treat as long as you re-do it every now and again. I used to apply it with a spray can and a compressor, but you can buy the pump sprayer which is quite good as long as you warm up the waxoyl first (bucket of warm water with waxoyl can in). I've seen Waxoyl in aerosols recently, but I'm sure that it would cost a fortune to do the whole underside of an Omega.

Wouldn't use the standard tar like underseal again, horrible stuff.