Hi,
I used to check my old Coachman twice a year.
For the roof: Clean old sealant with acetone and reapply new Dicor self-leveling to any crack, seam or screw head that looks thin. Poop it on thick.
For the sidewalls, lights, plugs and ports: Clean old sealant with acetone and reapply new Dicor Non -sag to any area that looks thin or cracked. Use a thin bead.
There is no reson to remove the old, just clean it with acetone so the new stuff sticks.
Both versions above are around $10.00 a tube. You will need 1 tube of each.
There are many here that used EternaBond tape on the roof seams for permanant results. I am going to use the EternaBond tape on my roof when I get my new unit this spring. This cost more, $100 + but is permanent.
Hope this helps.