After last weekend's fiasco, I've decided to take my extruder apart, at least enough to see if there are any obvious signs of blockage or damage. I also ordered a better (hopefully) hobbed bolt from arcol.hu, will certainly take macros when it arrives.
Taking the extruder off was not as bad as I feared, I didn't even have to remove the fan shroud. Helped by the fact that I got a proper set of hex keys at Bauhaus, it was simple enough to unscrew the two main screws and the D-Sub connector (plus unplug the rerouted wires).
The first thing I noticed was how there was marks on the hot end, as if something had been flowing down the next of it:
Once I got the appropriate bit for unscrewing the nozzle (slot screws? Really?), there was ... nothing special to see. I put it together again and tried to extrude to no avail.
I got a small amount of progress through following nophead's instructions, to the point where I could extrude into thin air. I noticed that the extrusion went a bit sideways, and sure enough, as nophead warned, it clogged up again when trying a test cube. The pin I grabbed was not thin enough to get properly in and get the gunk out, so I'll have to get a thinner one, or some wire.
In the meanwhile, I design stuff. Last thing: A ring light holder and reflecting lens hood for my macro lens. OpenSCAD is quite handy for that kind of thing.