Is $3,600 to repair a flat roof a fair price?

I purchased my house 5 months ago, and the sellers disclosed a new roof was installed in 2024. The inspector confirmed the roof was great at the time of purchase. Recently, I noticed water marks on my ceiling, leading me to call roofers. One roofer, who admitted limited experience with flat roofs, noted workmanship errors. A second roofer, from a company specializing in flat roofs, also attributed the leak to installation errors. He recommended a full replacement over repairs, which he called a 'bandaid'. I have a third roofer coming soon. I'm trying to contact the previous owners to identify the original installer and have searched public permit records, finding no permits issued for my house in 2024, though I'm investigating blanket permits. My understanding is that homeowner's insurance won't cover this, and most installation warranties are non-transferable. I'm exploring options, including pursuing the original company via Right to Repair laws.