Need bulb type for stop/brake light on ML320 1999

I don't have my owners manual handy and I need to replace the upper bulb in the rear drivers-side lamp cluster (this is the stop/brake bulb) of my 1999 ML320.
Can anyone tell me what bulb type it is and where I might find it (i.e. auto parts store, Wal Mart, etc). For some reason P21 comes to mind but I'm not sure.
Also, how do I get to the bulb in order to replace it? From the inside, how do I remove the panel, etc.
Thanks, Walter
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On 2004-10-11 08:12:09 -0700, w snipped-for-privacy@hotmail.com (Walter Cohen) said:

This should be pretty obvious... Go look and there is PROBABLY a platic panel that comes off, once you pull the bulb, then you'll know what kind you need :~)
Any autoparts store should have it.
Marty
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