Touché. I removed the lens on my X5 and upon VERY close examination I can see that there APPEARS to be a layer of glass over the sensor. That said...
A dust speck directly on the sensor (or underside of the glass) suggests that there's an open gap between the two. I would hit the lens with some dry air from a real air compressor with a moisture filter (not canned air). Start low @ like 10 PSI and work up until the speck is dislodged. It seems this would be easier than taking the lens apart. If you don't personally own that kind of compressor set up, surely you know somebody who might? That said...
I'm going to guess that the screws are treated with some kind of robust threadlock product like LocTite™ 271 or the like. If so, removing that screw is going to be nearly impossible. But if that's the route you're going to take, I would trust nothing but the best screwdriver money can buy. Ifixit seems to make some very high quality stuff. I haven't personally tried their stuff but they surely have a lot of endorsements. Wiha is a brand I own and have never had any complaints.
I wish I had better advice. Good luck!
D