Sheared Torx screw

[Wombat]

I have just noticed that one of the hub cap Torx screws has sheared (not by me, as I've never tightened them!).  Originally I thought it had vibrated out, but the body of the screw is still in place.
There's a film of oil all round the hub cap, presumably due to this, so my question is (I do not have the Speedhub manual with me to check) do I just need to extract the stump of the broken screw and replace it, or do I need to remove the hub cap completely and replace with a new paper seal?

(Asking  so I can order the parts now to pick up when I'm next at home).

[expr]

wombat, the film of oil around the paper gasket is normal and to be expected, the paper gasket is soaked in oil from the hub and therfore the vapours attract dust etc and show up where the oil is.

The torx screw can be extracted with the hub cap still attached, you need to accertain how loose the remaining threads are, factory fitted ones initially had no thread lock on and they are now fitted with pre dipped loctite 243.

Is any of the thread still showing from the top?

[Wombat]

'Film' may be a wrong word - Im fairly sure that oil is leaking slightly from the area around the sheared screw.  I have had some random oil drops overnight, which would be explained by the missing screw being in the 'down' position.

The only visible part of the screw is in the actual hub part, so it's going to be a delicate job to get a small extractor in there to remove it.
I'll obtain a Torx driver tomorrow to check the rest of them, but there is no movement when tested (gently!) with a small screwdriver.

My plan will be to replace just the screw, as the paper gasket should still be held in place by the other screws.

I'm slightly worried by how this has happened though - what stress has caused one screw to shear?

(As the replacements come as a set, I'll probably replace the others, just to be sure!).

[expr]

This has occurred with other people in the past due to the fact that the screws have worked loose (no loctite), you need to check the other screws to see if they are loose enough to cause just the one to shear.

If they are all tight you have a dodgy screw, i cant see it having been overtightened that's caused it, as you say you haven't touched it.

The way in which i would attempt to remove the remaining thread is to drill a 1.5/2mm hole in the screw from the flange side and either use a stud extracot if you have one or tap in with a small hammer a cross head screwdriver (small) or similar.