Ok, Just fixed this problem with my 1200 series thanks to this forum. The details: Just got new unit. Wife unknowingly used old base from our old 900 and it got stuck. Freaked out a bit initially and then, after some fiddling around, found this forum. Used the inversion and thump method which worked beautifully. Couple of points for future pilgrims: as mentioned above, put down a tea towel or similar. You will likely need to give it several thumps. They will need to be quite firm, but judicious. For me, I thumped three times and it just came apart. It was like magic because we could not get it to budge by twisting. Upon subsequent examination, the bases appeared identical where they engage with the unit so it seems that they should work interchangeably, but I found that the drive wheel on the older 900 series base showed significant lateral play compared to the new one and probably needs new bearing. I’m thinking this was likely contributory. Anyway, problem solved, peace and harmony reign once again. Thanks x 1000 guys.