Like Matt said... Search around.. Pads are a lot less flotation than a Bob simply because of placement. Sealing a mast isn't that hard. Or expensive. On every old boat I have owned I ended up just drilling and refitting all the rivets hardware, and sealing the plugs with fresh silicone while I had it open.
I wouldn't fly a bob just because with a sealed mast popping the boat up from turtle isn't a big deal, and often I have intentionally turtled just to take a break and pull it back up the direction I want to go. (I doubt there are many people who capsize more often than I do when playing around... heck last year I finished a race by purposefully flopping only the mast over the line.
But I also often have a bit of mud on my sails..