It's such a touchy situation.. If that latch isn't coming all the way up and you pry on it, it could lead to bigger problems, but if all it is is gooey seals.. You're in good shape. Is there film in it? If so, make sure it's rewound all the way before you do get it open - you could have a hidden gem in there
I own the K1000 - Is it possible to slightly compress the area where the latch is while pulling up on the rewinder? If there is no play I wouldn't suggest squeezing much. You could always use a A-1 oil or something around the door seals to soak out that gasket goo.. Though, you'll need a thorough cleaning afterwards to replace the gaskets. Of course, if it's not the gaskets and you manage to get it open otherwise, you'll need to new gaskets after a light oil treatment.