Changing the tumbler in my 300E was "easy", but took a long long while of wiggling the little wire tool around before I got the magic click and got it out. Probably more than an hour of fiddling, done in several sittings.

Also, although my "custom matched by VIN" tumbler came with a new key, my dealer parts guy said they don't always include it. It just happens that the way they make the tumbler is to make the key first and then match the tumbler to it. Sometimes they leave in the working key when they ship it, and sometimes not.