Dave,

I have recently done this replacement (tumbler WAS replaced only 1.5 yrs ago!). Depending on if you can still turn the key to pos I (then you are lucky) then you can follow the instructions on this link;

http://tech.bentleypublishers.com/thread.jspa?forumID=3&threadID=20922&messageID=214522#214522

I paid $$$$ 1.5 yrs ago when the key won't turn at all.

Good luck.

KC