Hello, I am a newbie but I did this work myself last year, so I will try to help. I use Manus Bond-75 (white) and Henry's (clear) on vertical areas ( ordered from Lichtsinn RV) and Dicor self-leveling on the horizontal sufaces. Old Dicor scrapes off easily, the silicon type is much more challenging to remove. My local RV repair shop suggested using WD-40 followed by mineral spirits to remove residue then some rubbing alcohol to remove that residue. It worked well but needed elbow grease! I also used those orange plastic razor blades (Ace Hardware about$2.50). I was advised to not be skimpy with the Dicor self leveling sealant, and don't forget to seal the screws on the vent cap and the refrigerator roof cover or any others you find. Also keep an eye out for any hairline cracks in the filon and run a wide bead of the Dicor if you do.
I hope this helps. Happy Travels!
P.S. I am not that familiar with compatibility to make suggestions with the silicon type, however new Dicor can go over old Dicor but I like to remove all of the old and start fresh (cheap insurance).