I have some 1970's fluorescent one bulb fixtures in my kitchen (old fashioned cove ceiling lighting with plastic diffusers mounted to the ceiling and wall at an angle). The fixtures are ceiling mounted close to the wall. There are a few different size fixtures and I have changed ballasts in some of them over the years. This particular 4 foot fixture has a bad tombstone so I am trying to get the cover off to replace it (and also to check the ballast). This is not thin metal like the new fixtures that you squeeze to remove. I see nothing holding the cover and thought it would snap off. No luck at all. I noticed two dimples in the metal sides of the fixture; one dimple at each end (and I feel the same dimples around back) so I figured that they must be there to tell me where the cover is secured. There is no give in the cover where the dimples are located (about 8 inches from each end of the fixture). Something must be there to release as I can't even remove the entire fixture from the ceiling without access. Any ideas? Thank you.

Some photos of the fixture would be helpful.

Thanks. Will post pictures at the end of the week.