What heat sink compound to use in a Musical Fidelity A1?

I'm doing some (hopefully) minor repairs on a 2008 Musical Fidelity A1. Removing the top cover reveals a 2" x 10" block thermally connected to the cover plate with white-silicon-grease-looking heatsink compound. There's quite a lot of it there, and I will need to clean it off and replace it before putting the cover back on.

What kind of heat sink compound should I use? My searches mostly turn up tiny tubes of compound to be used on CPU heatsinks. Or I see industrial materials. Any specific suggestions on what I should use? How much do you think I'll need for a very thin coat over that big of an area?