bought a 87 hi lo were ac unit on roof is starting to sag in the middle are the a fix for this also going to recoat the roof what is a good sealer to use was think maybe sta kool or kool seal thanks for the help

Sounds like you may have some water damage, either from a leak around the unit or from the unit itself. They are known to build up condensation and it doesn't drain properly.

Kool Seal seems to be the sealer of choice on the forum.

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"Ruben"
2404T, 2003 2500HD 4X4 GMC Sierra SLT Crew Cab w/Astro camper shell and 2003 Chevy Tahoe LE 4X2
Far West Texas