Thanks everyone I appreciate your candid answers. The main word I'm reading here is "plastic." My '99 Tip has always been garaged by me (and it appears that the prior owners also garaged it) and I also use a cover on it as I moved next to the ocean a couple of years ago.
Last year I had the car inspected and was told it is in remarkably good condition for a 17 year old car. Over the six years I've owned it I've replaced the top, front seats (wish Porsche had used thicker bolsters on the driver's side), suspension (M030 Sport), Big Red brake upgrade, intake and exhaust upgrade, IMS (LN ceramic) and RMS, respray and new windshield (insurance paid for both), 18" wheels and several other minor mods to interior.
Although I rarely drive it with the top up I'm not experiencing the plastic deterioration I'm reading about here but thanks to your inputs I now know what to keep a check on.
