Has anyone replaced the rear Hatch Seal?
 

In 21 years of working on MKIII Supras I have done many things but replacing the rear hatch seal is not one of them. They usually start falling apart on the bottom near the lock because that is where most of the force gets applied. The part number is 67881-14110 and I have a brand-new one for $88 delivered. There's not much of a groove to fit into the bottom of the seal. When I peeled the old one back a little bit, all I saw was a very small amount of gray gummy a sealant. Has anyone done this before and are there any tips to offer? Any particular kind of sealant or is it a Toyota dealer thing?

To my knowledge practically any of the quality sealants (I like 3M) will work to seat and seal your replacement hatch seal. Just make sure the lip the seal is seated on is clean and rust-free, and that nothing is messed up on the hatch which could damage your replacement.