Do NOT go there because you will void your warranty and risk damage if you do. But sometimes choices are not so easy.

For some reason, most likely because you thought you knew what you were doing and removed the IR panel in less than a proper air-filtered clean room, you got a mote of dandruff on your sensor. You did not notice it until you started shooting in bright light at f11.

So you go back to "GO" and do not collect your $200.

You take out the IR panel again and search for your little bit of dandruff and for the life of you it cannot be found because it is too small. You go for a blind puff of air but must put things back together to see if it worked and you find it didn't move or migrated along the sensor to a new place.

A little trick I used on the SI2K and this time round on the big URSA to get an instant view of whether the dust went away has been to cut a camera-throat sized disk of Weetie ( breakfast cereal ) packet cardboard of around 0.2mm thickness and poke a large pinhole in it.

The cardboard disk I place on the front of the camera throat. With the camera switched on and using a small LED torch, I shine light through the pinhole from about 70mm out with no lens fitted and voila there's the spot to be seen on the screen. You need to move the torchlight around a bit in the image to find where it is at.

A little puff of air and you hope its gone but now you can quickly discover if it has not.

Now comes the hard yards of getting that neoprene ring back in around the IR filter disk. The best method it seems is to use a non-metallic object like a plastic knitting needle or satay stick, centralise the disk in its place with the point.

Poke two parts of the ring into the groove at 180 degree intervals, then two more to make four at 90 degree intervals, using the flat end of the satay stick to draw the neoprene ring around so that all bows in the ring are equal, then keep-halving the bows until the ring is finally in place.

Be gentle. That glass disk is fragile. Do not use metal to poke the neoprene ring. You'll only chip the edge of the glass. This creates a stress riser which may later propagate a crack.

BEST PRACTICE. - Don't do it yourself but let BM have a go at it. They after all should know their camera, have the foolproof tooling to do the job in a heartbeat and a clean room to do it in.