You do have to go from underneath if you want to take the whole thing apart. The mast was (or atleast on mine) glued down with loctite before I purchased it, and a while back I was going to take mine off just to clean it really good and I ended up snapping the mast, radio reception went from poor to none for about a week....lol. $12 and a couple trips down to the dealer later, and I've got a new one.
Only problem on mine was when it snapped, the bottom part stayed in (b/c of the loctite) so when I got the new one I had to cross drill and make some new threads in order to get the new one in. So bottom line, go from underneath, it's a whole lot easier. I shoulda just taken the whole thing apart....but as usual I did it the hard way...lol.