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Might be worth stripping apart to see what the crack is. The spindle lock on my Dremel 8100 started slipping recently, I took the whole thing apart, used pliers to hold the spindle to get it loosened, cleaned everything, put it back together and did the screws that hold the housing together up a lot tighter than they'd been before I dismantled it and it works fine now.
Think the high frequency vibration of the tool had rattled the screws loose which was allowing the spindle to move away from the locking pin.
Buyer beware the Lidl dremel. I broke mine. First one sounded really nasty when the motor ran so I returned it. Second I snapped the tool tightening thingy, so pushing the button does nothing. I think it has a very low end locking pin assembly inside.
Course, snapped after 30 days thanks to minimal use.
Accessories have worked fine though!