I’m certified in GACO, but never sold one yet. I have 2 roofs, one MB and one BUR with 2-3 year old GACO on them. They will both be getting a fully adhered 060 EPDM shortly. Once you put down silicone you’re stuck on options. As far as depressions, a pond is considered and standing water 48 hours after rain. Most coating warranties wont cover ponding situations. If you’re serious about maintenance, make sure the roof is vapor vented. 2 way vents are preferred. Check all penetration and wall / parapet flashing details. Any repairs MUST be done with mod bit flashing cement, asphalt plastic cement will divorce and curl up in a year or 2. Use a leaf blower to clear debris.
For flashing, I don’t even know why tar is used anyhow - seems so old skool ? Is it because it’s same/similar expansion rate with SBS bit mod. I’ve used urethane sealants on similar expansion areas/sealing, and it last much longer - unlike tar which dries out and cracks.
I’ve looked in the roofing aisles…19 or 19 ultra seems to be the most popular ?
The flashing cement you need is called neoprene and you can get it at a roofing/siding supplier.