99% of RV roof fan openings will be sealed with Dicor, self leveling sealant.
"501" And that is the best sealant to reseal over the existing sealant.
You will need, mineral spirits to clean any dirt from the existing sealant , for a good bond. Just follow the directions on the tube.
$8 to 10 at most RV suppliers, while your on the roof check all seams for cracks , if you have a leak due to dried out sealant , it won't be long before you have another. Write the date of opening on the tube and don't use it if the tube sits for more than a year after opening.
Kitchen and bath , won't stand up to the drying effects of the sun.
Spray can " snake oil " may have its uses; JMHO . if it was really good , they wouldn't have to advertize so much.