Tracks and bogies for the most part on the tractor, if I had to guess it will be due for a new set of tracks. One suggestion if you buy a set of tracks is to go with a completely smooth track. We thought they were a joke but we got talked into trying a set and they do make a big difference not tearing up the stone base when basing in something. As for the screed, look at the blower motors (assuming it's a fuel oil heated screed), and the screed plates, and bull noses, and then check the large guide rods for the extensions for damage (large scratches and gouges). For the most part these screeds are fairly bullet proof and do not require being adjusted as often as other screeds. When you get the paver have a talk with the guys about wiping down the guide rods on the screed extensions with pledge a few times a week. Some people say it causes build up on the large guides but we were told by the original engineers from barber-Greene to do it and we have for years without any buildup or damage to the coatings. Good luck, they're good screeds and lay a nice mat and quite honestly I like the deisel heat better than electric anyway just make sure the guys don't over heat and warp the plates and you'll be fine.
Ps stay away from the new extend a mats, cat was outsourcing the manufacturing of them and our last screed had some major problems (the older ones are bullet proof) and that's why we made the switch to the Carlson ez-r2's.