Repairing a small crack in the roof of my camper trailer

If it were me, I would remove the old caulk, carefully, and get some self-leveling Dicor sealant/caulk. Clean the area good, make sure it's dry, and put down a generous amount of the sealant. Silicone sealant generally isn't a good idea for this type of application as it can make subsequent repairs very difficult.

Yup. Clean ALL the old caulk off and use Dicor.
NEVER use silicon!

Since part of what needs sealed is a vertical surface, you will need the NON SAG version of Dicor.
If you use the "self leveling" kind, it will make a mess and run down the wall.
Self leveling is meant for flat horizontal surfaces only.

I've used self-leveling on sloped areas without any problems, and that looked like most of the fracture was on the flat. But granted there is a bit on the edge. Self-leveling isn't like water and run downhill. :) But you do have a point.

Dicor is what I'd use, but either type will work for that repair. Self level would be best choice, but if I had a non-leveling tube already open, that will work too. A little paint thinner on my finger does a good job of leveling, when needed.

Use of painters tape will eliminate most of the messy look. Just remove it before the dicor starts to set up.

Jerry

Looks to me that there's more going on than simply a crack appearing. Looks like there's a large and a small crack. Looks like something structural is coming apart and maybe something was never fastened with a screw or bolt. Maybe there was a small crack that occurred awhile back and after a while of exposure to the elements, there might be some structural failure. I think I would check first before trying to seal it up.

Thanks, everybody, for your advices!
I think I will try to go with NON SAG version of Dicor.

For a crack like that, I remove the old sealant. I then inject URETHANE windhield gasket sealant in the hole to fill the gap. Then use the Dicor over the top. Doug

https://www.amazon.com/Tubes-Dow-Sealant-Adhesive-Urethane-Primerless/dp/B01DJKME0Q/ref=sr_1_12?hvadid=409942333383&hvdev=c&hvlocphy=9027230&hvnetw=g&hvqmt=e&hvrand=3659331111487500056&hvtargid=kwd-1102908166&hydadcr=24659_11410797&keywords=urethane+sealant&qid=1681135709&sr=8-12

dougrainer wrote:
For a crack like that, I remove the old sealant. I then inject URETHANE windhield gasket sealant in the hole to fill the gap. Then use the Dicor over the top. Doug

https://www.amazon.com/Tubes-Dow-Sealant-Adhesive-Urethane-Primerless/dp/B01DJKME0Q/ref=sr_1_12?hvadid=409942333383&hvdev=c&hvlocphy=9027230&hvnetw=g&hvqmt=e&hvrand=3659331111487500056&hvtargid=kwd-1102908166&hydadcr=24659_11410797&keywords=urethane+sealant&qid=1681135709&sr=8-12

Thank you, Doug. Am I understanding correctly that I need to remove this sealant (highlighted in green in the picture)? How should I best do it? Just cut it with a knife?
What are the benefits of using automotive glass sealant to fill cracks like the one I have? It sounds like something from a completely different field of application.

I'd remove "ALL" the black caulking, and start fresh.