Do DSLRs gradually go bad?
Shutter mechanism can slow down but still work, at least on a 20D. Mine would work fine at slow shutter speeds but as I increased the shutter speed it would be increasingly slower than specification. It showed itself as producing over exposed images even though there were no error messages. At first it was subtle and it took me a while to figure out what was going on.
My first clue there was something wrong was when I was trying to calculate the speed of a softball pitch from the shutter speed recorded in the exif and the distance of the blur on the ball. I kept coming up with 100 mph pitches, which is pretty much outrageous for high school girls. Upon further testing I noticed the exposure was also changing. Pushed to the limit it was pretty obviously not performing to specification.
My first digtial camera, the FZ-1 a bridge camera is still taking beautiful images for my sister-in-law. The first shots I took with it were in Dec. 2003. I still have alLike new Leica V-LUX 1 (FZ-50) that I got in 2007 that hasn't skipped a beat.