Wanted to jump in with another huge THANK YOU for posting this teardown. Found the thread via Google and it was very helpful for me in servicing a DC25. Spotted the unit out with someone's trash, figured I'd check it out as it would only cost me time to do so. Obvious problems when I first found it was that the power button plastics were missing as well as the screws that hold the power button cover on, it was missing the combination tool, and it looked like someone had been using it for cleaning up drywall construction.
On testing the motor ran fine but the brush head wasn't rotating. Got new power switch plastics just so I wasn't reaching down to the actual switches, found some usable screws to hold in place, and got to troubleshooting.
One tip I found for the power brush head, you can connect it directly to mains voltage to test. I took some 14AWG (I think) solid core wire, jammed into the brush head plug, and then ran via a lead to a switchable power strip. Switched on, brush head was working. So I knew I had a problem somewhere in the loom down to the brush head connection. This is where the teardown here came in, with it I was comfortable tearing into the lower bits. Took some head scratching before I found the broken wire, but it was where I expected it to be. In the area by the connectors where the wires are allowed to flex as the vac is moved up and down, apparently the white wire had snagged on the guide clip and snapped. Couldn't see it at first as the break was sneakily hiding behind the guide! With that found I ordered up a new lower loom section ($15USD of ebay) but in the meantime rearranged things and soldered in a repair. I arranged it so the repair was down the grey plastic loom holder so the section where the wires would flex had no stiff sections. So far working great and have the replacement part sitting aside as a spare.
That was a couple weeks ago, but your post helped me again today when I was wondering why the power head wouldn't lift up when I had the wheels locked. Found the spring-loaded plastic that was supposed to catch it was not on the post where it should rotate. Somewhere along the line (before I had it) apparently the screw that held this in place fell out or was removed and lost, and when I had things apart to fix the wiring I guess I didn't get that back in place correctly. Found a usable screw and washer in my parts bins and it should be good to go for a good while now. Could get a proper replacement washer and screw (DY-911106-01 and DY-910703-02) to make it right, IF I feel the need to spend $10USD for the itty bitty parts to do so...
So once more a very grateful thanks for sharing your experience. So many years later still helping people out. You deserve a nice pint for this!
But I do have a question to close this post... after putting the power switch plastics back in (which was fiddly) I don't think they feel like they should. On review of parts diagrams I've noticed there is an on/off actuation arm listed (DY-966031-01) that I don't see in my vac and didn't see in your photos. I'm looking at the exploded view here:
Anyone have any insight on this? The vac is working without and I can't find anything about how this fits in, but I'm wondering if the switches would feel more "positive" with that part in place.