As above, rust in the floors scuttle, rear arches/valence and fuel cap areas in particular.
If you find an 8v with pas your doing well, however all 90spec 16vs came with it, but check the rack as replacements are nigh on impossible to find.
Gear linkages suffer from wear but are easily sorted.
Heater matrixes, but most will have been done now.
Most headlinings will have dropped by now too, as the foam backing disintegrates, this also happens on the heater flaps so the air blows out of all locations regardless of the control setting. The only way to sort this is remove the dash and airbox and replace the foam covering.
Check for water in the footwells, the membranes behind the door cards split and let water in. Also the sunroof drain tubes can block up causing it to leak.
If your looking at a late 8v check the Rev counter and mfa work, these can be expensive to replace.
Mk2s are great cars, but even the latest ones are approaching 25yrs old now so finding a good one is getting harder. It might also be worth noting 5 doors seem to fetch less if your not that particular about it.
Good luck