Have 2015 Lincoln MKZ hybrid with terrible trunk leak.
Soaked up massive amount of water inside spare tire wheel well. Pulled out drain plug in bottom of this that went to outside bottom of car.
Took apart trunk trim on lid and inside trunk. Had wife run garden hose on top of trunk and I lowered or put down backseats to look inside trunk with flashlight, from back door/s.
Leak was coming from trunk lid, weather stripping all the way around trunk, and misaligned trunk lid.
Dried everywhere with towel and let car sit for few days in carport to dry out completely.
Drained lid by pulling out 2 mini plugs in bottom of lid. Used black and clear flex tape (from Home depot, $15 each for 2 rolls) to seal black plastic drain trim pieces on sides of trunk. I installed two rolls of 1/2" thick black rubber weather stripping self adhesive tape on underside of trunk lid edge ($20 each X2 from Home depot), all the way around. This lined up with the trunk's existing rubber weatherstrip to create a good seal.
Adjusted rubber stop legs (2 on bottom of trunk lid) and lowered trunk metal bar latch on bottom of inside of trunk that trunk locks or clicks onto when trunk is shut.
I now have to slam the trunk lid by hand to close it at the end of the automatic close. But creates an even tighter seal.
Caulked around black plastic trim piece on top of outer trunk lid with all weather clear silicon caulking (1 tube, $15 from Home depot paint section). (Use lacquer thinner ($20 from Home Depot or Canadian Tire, use sparingly on tissue paper to wipe up excess or to clean off your hands). Use tissue to smooth out caulking while it's wet. Let caulking dry for few days. Then caulked around top edge of black plastic trim piece on top underside of trunk lid. Let dry for a few days. This stopped water from going inside of trunk lid.
Installed more weather strip tape on edge of black plastic drain trim pieces on both two edges of trunk, to line up with trunk lid.
Put drain plugs back in, on bottom of trunk lid and in spare tire wheel well.
Put trim covers back in. Ran garden hose again. No more leaks.
Once trunk weather stripping begins to get bit flatter, will likely have to readjust trunk latch metal bar or rubber stops on trunk lid.
Wife discovered you have to put original trunk rubber weather strip on top of black plastic drain grim pieces on side edges of trunk. Then we put Flex Seal tape around the drain trim pieces and on those 3 black round fasteners on each side. Leave bottom of trim drain pieces open, so any water that gets under drain trim pieces can escape.
Could not believe how much water was coming in. Was like a shower...drip, drip, drip. Was so much water, it caused check engine light to come on. Once water was f
removed and trunk dried out, check engine light went off.
Had to replace the regular 12 volt car battery, due to the excess moisture. Battery died and we got locked out of car. Had to use emergency metal valet key to get into car, then put down back seats to crawl into trunk to access trunk release pull cord to access battery in trunk. Was about $400 for new car battery, from Lordco originally, but I got it half off from a sale. Is a specialty battery for hybrid vehicle's and you have to have it programmed or reset into car's computer by a mechanic with a code reader, or it will keep going dead and you will have to jump it. My friend is a mechanic and has a $2000 code reader, so he did it for $25, and it only took him 5 minutes or less, to reprogram the battery and computer so it was reset.
Good car, great mpg, gots all the bells and whistles, including built in radar detector, and massaging seats; but, real real shitty trunk design.
Thank God for smart wife, otherwise, we would all be lost.