I can almost guarantee he had a leak somewhere if he soliconed it. Its a really really common thing to do because the rubber sealers WILL go bad and are a huge pain to replace IF you can even find a replacement.
Yes it is very easy to remove the silicone. Just find an edge and start pulling. If they did a good job it will come off all in one swoop. If not though you might have to go back with your finger nail but it wont damage the paint or anything.
What I believe to be a "proper" fix. My method is cheaper, easier to remove, and looks better but is harder to apply. I use plasti-dip across my whole roof. Its only like 4 dollars a can from your local store or order it in a special color for a little more online.
Simple to put on and take off. Tips on spraying. Tape off windows and door seals but it doesnt have to be perfect because if you mess up the plasti-dip will pull right off.
Just like spray painting only you REALLY have to layer it. First coat just make a thin layer. second coat make a little thinker but not much. third coat you want to go over your previous layers and fix where it may be thin. You still should see the color of your roof at this point. fourth coat just a real thin layer and the last coat you want to do it think.
DONT worry about if it starts to bubble a little where you sprayed. It will even itself out as long as you dont keep spraying on that spot. Last two layers will be touch ups. If you see color, spray a coat over the area pretty thick.
Remember to spray the sunroof gasket too since its the whole point of this. I just sprayed over the whole window to make it easy.
Each coat should only let dry for about 10 minutes till your done. Once your done, let it dry for about an hour. Next summer, pull up a corner and the whole thing will pull right off
