It just so happens that I am selling a pair of headlights on ebay. ZERO yellowing, melts, or cracks.
http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&ih=017&sspagename=STRK%3AMESE%3AIT&viewitem=&item=270076928467&rd=1&rd=1
By levelers, are you refering to the little bar in the headlight housing that looks like a little ruler? Look below:
I'm not sure, but I don't think there was a year that initiated a lack of amber, rather it's an option maybe? I see amber on all boxsters on ebay from 97 to 04.