Rust!

Rear arches, battery tray, floor pans where the seat bolt up, front floor pans where they meet the sills, area around fuse box, scuttle, front inner wings, bottom of doors, door that sags a bit could be a rotten A post, rear floor pans where they go up in the corners and finally the front of the rear arch round the back of the sill...... Other than that they are fairly rust proof!!!

Other things to watch for on the engine are tappets and cam wear out, blue smoke on start up is valve stem seals.

Never managed to blow a gearbox on a xr.....(blown plenty of rs boxes though) so this should be fine, just check the driveshaft seals as running it low on oil won't help!

Dashboard top will most likely be cracked on a mk3

Finally Check everything electric works as I managed to burn the loom out on my series 1 and it took me DAYS to repair and finding a replacement loom ain't gonna happen unless your the sort of person who rolls in dog shit and comes up smelling of roses!

Also finding mk3 trim these days is a challenge especially if you have the one with the red piping rather than blue. So if the car is in bits make sure you get EVERYTHING.

Good luck and they are good cars if you find a solid one!