You definitely had a bad experience with car with sunroofs, GorehamJ.
Sunroof is a feature I can’t live without, especially that I do most night driving. The nice and cool breeze from a sunroof/moonroof is something to brag about. lol.
But yes, sadly, when they don’t work as should, the pocket suffers.
I’ll pay money to avoid a sunroof, takes away needed headroom for me.
This isn’t sunroof or convertible related, but…
We had a 2012 Honda Odyssey with the power sliding doors. Within the past year or so, the doors got a little wonky. Sometimes they opened, sometimes they closed, sometimes they beeped and reversed for no apparent reason. It was getting to be very annoying for me and my wife (especially the wife). I asked my regular mechanic if he could take a look at hem. He gave me a firm “no, we don’t work on those.” So to the Honda dealer I went. For a $200 diagnostic fee…they wanted to replace the motors and everything but the doors themselves for around $5000, I think it was. Bit of a shock.
For that and other reasons, we ended up trading in the Odyssey on a Pilot a few months ago. It’s great having 4 real doors now. Power sliding doors are great…until they go bad.
I once had a vehicle where you couldn’t open the ashtray if the shifter was in park!
Does this help you at all O.P,? 
Tester
From the forums it sounds like the most likely issue is the “roof rack” or luggage separator is in the wrong position. There is a way to open the trunk manually but you can only put the key in one way and it does require force from what i’ve been reading.
TLDR: I’d start with the simplest thing - check the trunk arrangement for issues. As @wolyrobb points out.
About 5 yrs ago I picked up an '06 SAAB convertible. It was really cheap (largely due to high miles and not great TLC over the years) and my wife always wanted one. And she does love it (a lot more than she loves me for sure). But I was trepidatious. They’re pretty complicated, and didn’t want to have to deal with fixing it’s issues.
As of now - knocking wood - it’s caused me very little trouble and has brought the wife much joy. The point is… it’s “smart” (complicated) enough to tell you if something is amiss with the trunk space when you want to put the top down. We usually learn this on the way to the beach…time to relo some items to the back seat…Maybe the Muranos are just as “smart?” IDK.
The other simple thing (always keep it simple until it’s time to not) is what @texases mentioned about at least making sure all of the mechanisms are clean and lubed. Then move on…
I think the OP might not be coming back, btw.
Visit a couple of inde repair shops in your area that specialize in Asian cars. Someone there may know a good place to get a bid to have your convertible roof fixed. Of course most any shop in town will fix this or get it fixed for you, handle the whole thing soup to nuts, provided you pay them enough cash up front.
Most ‘auto repair’ shops won’t touch it. The OP needs a shop that deals in repairing convertibles, I put that in Google maps and several ‘auto upholstery’ shops popped up. I’d do that in the OP’s area, then read the reviews for shops that deal with similar problems.
Might be a micro switch that’s stuck or bad, For those familiar with the car wizard he runs an independent shop in Kansas that works on a variety of cars.
What is this? Really, a Convertible Crossover? What crazy Nissan did the CAR WIZARD get in his shop? (youtube.com)
One generation of the Saab 9 (9-3? 900?) convertible had the microswitch problem from new. I knew two owners that successfully had the dealer buy them back under the lemon law.
It’ll likely take a dedicated shop and $$$ to fix this Murano.
