Body seam repair and products?

[KBM]

I had a leak on a weld seam behind a tailight, partner fixed by using epoxy putty, and so far so good, it is stemming the water ingress but I am concerned as this stuff is very brittle and when the temperature drops it may crack or not withstand vibrations of the car moving well?
Am I ok to leave it or better take it off (if even possible as rock hard push into cracks) and replace with a flexible automotive seam sealer? Is there a good seam sealer you can suggest? Thanks

 

[novocaine]

Tiger seal. nothing is better. I must have run hundreds of metres of the stuff over the years and never had a fault or issue.