550 changes in years produced

JRV and everyone:
I seem to be leaning more and more towards a previous owned 550 Maranello. I was wondering if anyone knows the minute differences between the years. I have not been able to find much literature yet differentiating the years.
I do notice that I have not found any shielded cars prior to 01. I am thinking an 01 car with shields and fully optioned could be a very nice car to have for the long term that could be used frequently. I am thinking by being very selective in my search for the right car over the next twelve months might pay off and while I look I think they will come down in price also a little.
Any more input is greatly appreciated and thanks for indulging my novice inquiries. As for service, I plan to get a full service manual but with these new cars it seems more of swapping out computer boxes than like fixing old cars.
It's funny, but when I was sixteen I worked at a large Ferrari dealer in Chicago and started there by sweeping floors to work my way through school. By the time I left there I was prepping the new 365 gtb4's and 275 gtbs and tuning them along with pretty much everything. I have wanted one since then. It 's about time to indulge myself, I can hardly wait. I just wish the had the same window stickers
gary