Ran out of distractions and excuses so I finally got on the roof and got it done. Slathered it on there nice and thick. The roof didn't come clean but there was nothing coming off when I'd wipe it so hopefully the sealant still sticks
I know a day late and many dollars short.
Well you should be set for a year or two before the vent starts leaking again. On RV's, Mobile homes, and trailers this is the "temporary patch" for 95% of the people. If you want to fix for a lasting repair you need to do a repair and not a patch. Most people can do what you did because they just do not know any different. The manufactures labels make the products sound like it is better then sliced bred.
Truth what you have done is is like paint a old wood sided house without, scraping, sanding, pressure washing and removing the old paint. The old dry products used below the product you put on top of the old old product will lift the new product on the top!
The proper lasting fix is to take the time and remove all the top roof coating (thick paint), remove the screws, and vent. Then remove the putty tape (Generally a gray putty) clean the flange (top and Bottom) and mating roof surface. Yours looks like it has the plastic flange. The plastic when screwed down generally will crack from over tightening when installed. If it is cracked replace with a new vent with aluminum mounting flange. Get some poly butyl gasket sealant. This comes in rolls of different width and thickness ,You will want 1" wide X 1/8" thick (No wider or thicker!). The putty tape will rip apart if stretched (a 6" piece stretched over 1 inch will rip with a jagged rip around 70 Degrees F.) the life span on a roof application is about 5 years max. The poly butyl at around 70 Degrees F. (a 6" piece stretch over 3" and not rip). The life span of the poly butyl on a roof is over 20 years.
I would not recomend using any roof coatings! The one adheasive/sealant I have used in this applaciation is a Polyurethane with a exposed to the weather life span of over 20 years. The true fact it is excellant, but a bit hard to work with. (If it dries on your skin It will come off in about 4 days when your skin serface cells die off under neath it.)
Note: Using any products all need to have a clean dry serface to bond with. Like Putty tape it has boiled linsead oil in to to keep is soft and plyable. When it is removed it can leave a oil substance behind. If nor removed the new product will m=not adhere to it. The same thing with many paints on factory painted aluminum. This glousy paint has a wax built into it. For this reasion that is why I recomend the One part Polyurethane.
I only would use 1.25 cases of Vulkume (also available in a brush on), One part Polyurethane a day and 300' to 350' per day of poly butyl per day. You need good ventelation if used inside confined spaces. Read safety warnings!
I know a day late and many dollars short. I do not want t take this as a negative post, I just want to educate people.