Blockage in the heater matrix - heater still worked but an annoying "trickling" noise (water) all the time when on the move. Quite expensive to fix - dashboard has to come out etc.
Head gasket blowing (reason for sale). There wasn't any evidence of water/oil mixing (cream like substance in the engine), but it showed in the performance and the garage confirmed. Again, costly to fix.
Baffles in the standard Vauxhall exhausts - they break up internally and you get a rasp/rattle at certain points in the rev range.
Rust! (speaking from experience with my GTE). The door bottoms rot from the inside out (check), the rear arches do the same (check) and the bottom of the tailgate also (check). Any signs of rot/bubbling here, walk away! If it is okay at these points then the first thing you've gotta do is Waxoyl it, the above points in particular.
The early GSi's had the more temperamental Bosch Jetronic management (same as the GTE), but the later one's have an Ecotec (?) system which is MUCH better and refined.
There are a few knocking about on L-reg plates. These are very much sought after as there weren't many registered on an L. Also, the Silk Violet metallic colour is VERY rare and are quite sought after.
You must Waxoyl them (see above) or they WILL rot in a spectacular fashion if neglected!
The ride is a bit jolty and unrefined for my liking, but I am a Nova enthusiast so I put up with it.
The gearbox needs TLC. Neglect/abuse it and you WILL have problems. One of the key problems is engaging 1st gear when crawling along. Get the gear linkage adjusted on a regular basis - this will help.
Anyone thinking of buying one (GTE/GSi models in particular) feel free to contact me at email@example.com and I'd be more than happy to answer any queries.