I didn't find a good solution. Long term, a high polished aluminium plate requires that you are very careful. When doing the mounting and soldering I was very very careful and worked pretty slowly with a blanket underneath. I treat my Crack with great care.
I used Autsol a couple of time during the sanding process, just to make sure that I wasn't missing any scratches from the coarser paper. For example, before going to 1200 from 800, I would give it a polish with Autosol just to make sure that the 800 paper successfully had removed any marks from the 600 grit paper and that the surface was even.
It can be wise to do this a few times, so you don't end up working your way to 2000, go into polishing and find a 800 grit scratch.
After 2000 I went over the plate about 2-3 times with Autosol, about 2*2 inches at a time (in circular motions).
Hope this helps.