Bob, there have been a lot of complaints about taking off the hubcaps on Base Model wheels. Evidently they don't come off easily. Several have reported that they broke the plastic hubcap in the process. Hopefully your removal will be easier. I'm late for work this morning. I'll research it for you this evening (no Internet at work) and get back to you.
DB aka Basset Hound
Pics at:
http://members4.clubphoto.com/don284358/