we left out clean, polish and dry lube the mating surfaces...If it's one of the ones with a plastic ring that turns and adjusts height we've recommended using heat to at least 4 or 5 people that had ones that were stuck and all of them were successful. at getting it to turn. A hair dryer like Stick suggests will work given some time. If you use a heat gun use it on low power so that you don't damage the plastic. If that isn't the problem then a photo would help and you can post one from your own hard drive by using the Go Advanced post option.
And a soft rubber hammer to coax it along...better yet, buy a new Bosch!use two hair dryers, position them 180° to each other...
you know that most everything is made in China, right?. they just change branding, and a few parts to make a new brand.. unless you find one that says "Made in U.S.A." else they could be "Assembled in U.S.A." from imported parts!..And a soft rubber hammer to coax it along...better yet, buy a new Bosch!