This was the most time-consuming project I have done on the LD. I should have ordered a new rig after 5 years. That way I would never have had to do maintenance.
If you decide to do this, you will need a hot air gun and oscillating tool. Harbor Freight quality will do nicely. The sealant may look hard and brittle on the outside, but it is still gooey underneath. I think that is what makes it a good sealant. Heating the sealant while working it with an oscillating tool with a sharp scraper will make the job go faster.
There may well be a better way of doing it, but this is how I did it.
First, locate the head of any of the 28 hex screws by removing sealant with an oscillating tool. After finding one, I used an extension on the socket wrench to clear the fan frame and to allow me to put my weight on the screw to avoid rounding the head. That’s just not something you want to happen, With one screw out, measure 2.25 inches to locate the next screw and repeat 27 times. Allow 2 to 4 hours for this.
Next cut the horizontal part of the flange with the oscillating tool right where it makes the corner of the vertical part of the flange. Now with a pry tool, such as a screwdriver, separate the vertical and the cutaway horizontal sections of the flange in the sticky sealant. Allow 3 hours for this task.
Even after cutting away the horizontal from the vertical, I was still not able to pull it up. So rather than spending more time prying, I put a bottle jack on the floor with a 2x4 reaching to the fan. It popped right out.
Finish removing the sealant on the roof and clean the surface by wiping it down with MEK or Acetone. I found that MEK works and smells better.
Installing the new fan. I put down a bead of Dicor covering the screw holes. That was a mistake as I could not find the holes, so I had to make all new holes. If I did it again, I would put blocks of wood under the fan to hold it up an inch, then start four screws. Then I would put down a bead of Dicor. Maybe by having it aligned on four holes the others could be located.
Anyway after getting all the screws in. I quit. I wanted the Dicor to dry. Two days later the Dicor was still a bit gooey, but I covered the top of the fan frame with Dicor extending it out an inch or so from the frame. Just the way the Mothership did it.
Larry Wade uses 3M 5200 FC [Fast Cure] rather than Dicor It lasts forever. I had Dicor on hand.
I sprayed the roof with Ford Oxford White where the oscillation tool scratched the paint.