Eternabond Tape and
Dicor Self Leveling Lap Sealant are about the best products for repairing/maintaining RV roofs.
Eternabond is a one time repair. It will last a long time.
Shop around for the best prices.
Remove the old sealant, if it's loose. If it's sticking okay, just leave it and go over it with the new sealant.
Use a heat gun on LOW and a plastic putty knife to remove the old caulk.
Clean the area well before applying the new caulk and/or Eternabond.