I have a 98 xj8 that the previous owner parked under walnut tree. Crap from the tree got into the mechanism then she closed the sunroof and broke some of the plastic parts. I want to remove this one and replace it with one from my 98 xj8l donor car. Has anyone dealt with this before?

 

Not so hard. Remove the headliner and then unbolt the entire pan. It then drop dpwn. Of course remove the 4 pipes in the corners... Refitting is the opposite way...

 

Are there any tips on getting the headliner down. These cars have a lot of plastic parts and I don't want to break anything.

 

If you do a search for headliner replacement, you will find a few threads with detailed instructions and photo's. There are also you tube videos under the same search criteria. Since you are going after the sun roof I would recommend you remove the front seats completely so as to not have to stretch around them.
If you have a donor car for the new sun roof mechanism I would practice on it for the removals first.
The four tubes mentioned in the earlier post are the drains for the sun roof. They are not watertight. Make sure they are clear and free flowing before putting everything back together.
One last tip invest in a cheap plastic set of trim removal tools. They will help in getting the trim apart.

 

I took your advice Vern and removed headliner and sunroof from the donor car first
Googled xj8 headliner removal and watched a u-tube video of a gentleman removing the headliner. It came off fairly easy and I didn't break anything. The sunroof came off easily too but the PITA was trying to get it out of the car. Dummy me I didn't follow your advice to remove the seats.
This weekend i'm doing the switch to the other xj8. This time I WILL take the seats out. I usally find a couple of dollars in change when I remove the seats, another bonus for removal. Thanks.

 

Sounds like you are over half way there and doing fine. Glad to be of help.