Rust. Rust. And more rust*
Have a look at the club 80-90 wiki, used to have a good checklist for buying.
* body rusts from the inside seams out, be wary of any van with filled seams. Look at the front to rear Waterhoses early vans have metal ones which rust, later ones are plastic but the ends can deteriorate and leak. 1.6,non turbo diesels are very very very slow. Windscreen often leaks and rots beneath the seal. Condensation trapped inside by insulation causes the bottom of the silks to rot out.
Buy on body condition only, everything mechanical can be sorted easily rust repairs can get complicated and expensive quickly