The car overheated three times. Each one it was repaired by a reputable dealer, and I don't think I was cheated (though you never know). The first time happened in a country road at around 80 kilometers per hour, having prepared the car the day before for a long trip, and with around 30000 km on the car.
The last time I decided to sell it, as the dealer said it needed at least a ring job, perhaps a complete overhaul.
The camshaft was worn round quite early, with the valve actuators all, but gone. I have been told this is a common problem with this engine.
Many interior parts kept falling, interior handles, trim, and such. Upholstery wore out very fast.
Clutch went early, around 60000 km.
Noisy and clunky gearbox.
Minor electric problems.
Monzas were Brazilian GM J-cars (Chevy Cavalier, Pontiac Sunbird, Opel Ascona, Vauxhall Cavalier, Cadillac Cimarron, Isuzu Aska... well, there were a lot of them). The car had very nice styling, easy access/egress, comfortable seats, nice upholstery which wore out quite early. It was quite expensive while not having even power steering, but seemed nicely finished at the time of purchase.
Fuel consumption was very high, around 7.5 kilometers per liter around town, marginally better on the highway.
Due to the overheating problems, along with early clutch wearing and gearbox noise discouraged from using it and from buying a similar car again.