I have got an old 5d from a customer with the definite wish to change the shutter. As the body had more than 380000 exposures, I have replaced the shutter on a brand new one.
After assembly, the mirror blocked during exposure. I asked the customer about the symptoms from the past – as a blocked mirror has to produce some half dark photos. He told me, that this is true – and on another service advised him to replace the shutter. Fine.
I have seen a deformation on the mirrors frame, so I disassembled the whole body again. And the mirrors frame was broken!
As the mirror itself is not available, I decided to glue it. I use the Loctite 3090 two component cyanacrilic glue. Expensive, but quick and strong.
Yes, the glueing is a little bit, …. too visible – but in this case the MOST important was, to make it as strong as possible. The mixed glue is tacky, hardenes quick, so this was the maximum which I was able to commit. Before glueing I cleaned it very thoroughly with some special pure white spirit.
After assembling back I have seen, that the gears were very loose. I talked to the customer again, and I replaced them on parts from a donor.
The black coloured grease is the material of the pinion and the axis.
So be careful: half dark photos can be caused NOT ONLY by a broken shutter.