So the butyl tape goes on the inside upper part of the rail and then you seal the gap where the rail meets the roof? Do I have that correct?View attachment 3013View attachment 3014I used a combination of butyl tape & 3M UV 4000. I spoke with a 3M chemist and he said 3M 4000UV was the best "over all" for roof applications . I put the new tape right where it was originally then a thick bead of 4000UV above the tape - probably overkill but I'm allergic to mold so I'm going to all lengths to keep coach dry The real key is getting the rail completely seated into the groove. In my case it took A LOT of work because they did such a cruddy job when they manufactured it.