Resurecting one of my old posts. I think I have this mostly solved finally and with a little more work I will have it completely solved.
It took a few sessions and a couple different techniques but I was able to remove the huge pile of caulk and the original vulkem sealant. Paint stripper worked to remove some of the latex caulk off the top but it was slow going. So, I used a heat gun to soften the caulk and then dig under it with a scraper. Once I had removed the majority of the caulk using the heat and scraper I was able to use stripper to get it down to bare metal.
After all the junk was removed I used Eternabond Aluminum tape (4" wide) and sealed the vent. I had my wife watch the vent inside of the trailer and I soaked it (really soaked it) with a hose. There is one very small drip at the center of one side and that is where the vertical side of the vent that sticks above the roof is cracked. I will apply more Eternabond up the sides of the vent and I should have no leak at all.
At this point I am thrilled with the results and look forward to not having to worry about the leak the next time we are camping and there is a rain storm.
1993 34' Excella 1000
2005 Dodge Ram 3500 Diesel
(No it doesn't have a HEMI in it)