2015 Gen Three Prius Trunk Lock Issue

It just unbolts and if you follow the wires back it should unplug before you do all that what does it look like when you're inside the hatch and you just gently bring the hatch down this is stuff line up there's also a little trigger that you can push with your screwdriver or something from the inside of the car should it decide to latch when you pull it down this should be a pretty straightforward endeavor inside of that metal housing is a spring that it should not take a slam to make it happen You should be able to gently put the hatch down and then pull on it and that thing should snap in You can also use the head of your Philips screwdriver or the shank of your Philips screwdriver push it into the door lock and gently push down and the door lock or latch should swing to the catch position sorry the trunk latch. You should be able to do this inside the rear hatch and gently pull how much force are you having to put on your screwdriver shaft to do this You're just mimicking the metal hoop on the hatch with your screwdriver shank You see how easily that goes click so maybe you need to loosen the catch which is on the hatch and move it down a little bit crack the bolts and tap it gently let's move it a little bit tighten it up see if that gets you where you need to be You should not have to be slamming anything these cars are thin enough sheet metal as it is you'll start to bend things

 

You got the gunk out - but than you used grease. If it's the grease that's keeping the hatch from locking. can't think of why that would be but ya never know. I'd try a spray of PB Blaster or WD40 on the grease near the latch actuator than test again, rinse repeat a few times to see if it makes any difference. You can always shoot some more grease in there if thinning out what;s there now doesn't work. My first thought was you cleaned out the gunk, than sprayed in some gunk attractor. Lubeing those locks and actuator things is never easy once they start attracting the goo and or slime.