Need Seam Sealing Recommendations

[Okiestreamer]

We have a few seams we suspect are leaking on our '74 Sovereign and would like some advice from those of you with experience sealing seams.
What products do you use and any other recommendations you may have for the best results?

Also, on the second pic, what is the black object next to the polarity light?

[r carl]

I put tape on each side of the crack and rubbed-pushed gray Vulkem into the seam, worked perfect.

[eljay]

Apply the blue tape on each side of the seam leaving about 1/8 inch on each side. Use the trempro/vulkem to seal the seam. Cut the tip at about 20 degree angle. Push the vulkem/trempro in. Use the tool to further push it in and smooth it out.