Being a sheet metal worker by trade I probably have a bit more access than most to the materials but I have replaced several leaking drain pans on otherwise good systems. My parents just received a new 16 ga fully tig welded 316L stainless steel drain pan for their evap coil. Expected drain pan life expextancy UNLIMITED friends/customers only receive lite gage galv pans, life expectancy 12 to 15 years LOL. Point is that if you have know someone that works at a sheet meatl shop, they can whip you out a new galv one out in just a few minutes, bring them the old one for a sample to build off of. Note: it may look like you cannot remove the pan but with a few cuts in the right places with metal snips the areas where the piping goes thru the metal can be cut away, that part is not needed anyway so don't try to build it back in just delete it from your new one. I cannot think of the name of it but have used a water proof clear caulking product that is used for marine purposes, (nonsilicone) it will hold for along time if you can clean the metal enough to get a good bond.