[donal]

The stay that the check strap attaches to is prone to breaking on the 850.
This results in a loud double clunk each time you open the door. The spot welds weaken and break over time. I followed someone else's advice to repair mine. Basically, the door comes off and a bolt or bolts is inserted to effect a repair. It takes about an hour in total.

See picture.

You will require:
An 8e torx bit and driver (or a 10mm? socket, depending on model) to loosen the locking bolts on the hinges.
A torx bit (can't remember what size) to undo the check-strap from the stay. Also, a very small torx to undo the electrical connection.
One or two 6mm bolts with washers and nuts (M10).
Some loctite.
Drill and a 6mm bit.
A jack is useful to lift the door up off the hinge brackets.
An assistant (to help with putting door back on)

Open the window.
Undo the electrical connection (undo the tiny torx screw).
Then undo the check-strap to door stay torx bolt, and separate the two. Slacken off the bolts which lock the hinges (either 8e torx or 10mm? bolt)
Use a jack with padding to lift the door a little.
Once its started it should be easy enough to lift it off (with window open) Plan in advance where you will lay it - it is very heavy! (No wonder these cars are so strong, last so long and use a bit more fuel than most!)

Drill a 6mm hole(s) through the pillar and the stay's back-plate (close to where the spot weld(s) have failed.
Prise out the rubber bung which is next to the stay to access the threads of the inserted bolt.
It can be tricky to get the nut on the bolt, so wrap some sticky tape around your finger to prevent it falling down inside the pillar.
You will find that a 10mm spanner with a bend put in its end will allow you to grab the nut in order to do the bolt up tightly.
Don't forget to use a little Loctite.
Put everything back together.
You will find that an assistant will make the job of sliding the door back on its hinges a lot easier. (While you're at it put some grease on the exposed hinge pins)

Hope this is of help to someone. There is a better write-up with more pics somewhere else. Try Google.