OK, an update. I was visiting friend who'd not yet seen the car and was showing it off, and when we came to the trunk lid needing the key, he said, "I've got something for you to try." He handed me a little bottle of something call Strike Hold, which is apparently a super-duper penetrating oil. This past weekend I removed the latch assembly and spritzed the magic potion into every crevasse and seam I could get to and there was no change. Heavy sigh, reassembled and resigned myself to keep using the key, or maybe order a latch on eBay. The next day, though, the latch works perfectly!!! It fully releases! Phixt!!!! Now we just hope it's a permanent fix...




EDIT: Well, poop! No sooner did I post this than it stopped working again! Worked for three days, then goes back today to not unlatching fully.

EDIT II: OK, it's working again this evening...
Back in December I posted about it works if it's freezing out, but not otherwise. So it appears it's still temperature-sensitive, just at a higher temperature. It's been working all week, but it hasn't been out of the garage. Today it was out and about, and the day here was sunny and in the low 80s, and that's when it didn't work. It worked this morning, but not at lunchtime. This evening it works again.

 

Resurrecting old thread.
I have similar issue as OP.
My boot latch motor stopped working; so I ordered one from e-bay, seems to be 'refurbished' as there is secure paint on screws and label "warranty voided if..." Though e-bay description said USED.
Any way, 'new' lock assembly from e-bay works just as what OP described some of time. From fist glance, temperature seems to be a factor; when car is in a sun for a long time ant temperature 90F and above, stationary or moving, the problem is developing; I have not found problem manifesting itself at temperatures below 85F.
I need to find time to do some research if it may be worth to make one out of two.
BTW @jonpalley nice video!
Thank you!

 

I've replaced mine, about a month ago, with an eBay unit, and it works fine, pops loose properly when it unlatches, no key required. It makes much more of a difference than I anticipated! it was also less than 200 bucks, less than when I'd looked previously.

If you can return yours as not working and try again, you'll get one that works. Depends on how it was listed originally and how long they accept returns, and if you have to buy another first before removing that one. Little fiddly details...

 

Yes, I did ask seller to take it back. Listing was 30 days free return.

 

It's not really worth 250-300 bucks for it to not require the key. If it actually fails to latch, then we'll look into replacement.[/QUOTE]

I got one off evilbay for my 09 Portfolio in June of 23 for less than $115. NOMO Auto Parts generally has good used parts.

 

Never mind. Should have read to the end. Be nice if the link in the weekly email went to the last post............. Oh, well. Another cup of coffee...

 

jonpalley posted a very nice videos of taking apart trunk latch.
Here is another way of troubleshooting this problem, it dies not require taking latch apart, for troubleshooting, but it requires access to $300,000 piece of equipment


Naked metal parts in position but plastic removed

Brocken and dislocated gears; last stage of gearbox

good gears in second stage of gearbox

I know what caused it! was in a rush and had bunch of loose closing laying on top of lounge chairs in the trunk. I was too busy to spread things around and as lid came very close to be closed... I just 'helped' it a little.
So, I spend XXX time more fixing this issue!
Now I need to find a way how to 3D print broken gears and I will have good working latch again.

 

I you are into 3D printing you may have heard of Fusion 360 (CAD program). It does have a built-in plugin that you can use to automatically create a gear given some measurements. I have not had the change to need any plastic gears but that is where I am going if I need any. I have created a few simple, specialty tools that make my life easier in the shop.