My 120Y has never had any problems apart from general wear and tear and from my continuous abuse, which it has held up to quite well considering how hard I cane the poor car. Although the problems I have had which I have caused, I have stated below for interest to anyone who thrashes a 120Y.
About two weeks ago I bent a rear wheel (lucky I didn't have my mags on), wheel bearing, brake hub and axle. I received this unfortunate damage by going sideways around a corner and unexpectedly having to avoid a car, resulting in hitting a curb quite hard. This did not cost anything to fix because I have heaps of spare Datsun parts at close hand.
The suspension and wheel alignments stuffed up due to already worn suspension from old age, but also provoked by general everyday thrashing and often weekend thrashing. I still haven't fixed the front suspension because I don't have enough money, but I replaced the rear shockers with Nissan/Datsun Bluebird wagon rear shocks (because my 120Y is a wagon).
I am soon going to replace the whole front suspension with Datsun Stanza suspension (whole struts including springs, brakes etc, radius rods, steering arms). Replacing all these is a relatively easy job for any slightly mechanically minded person, and only takes a few minor modifications eg. drilling a few bigger holes. The result of this modification is very much improved handling, braking and a very firm ride due to the fact that a Datsun Stanza is a fair bit heavier that a 120Y - approx. 300 kilos. With Nissan/Datsun Bluebird rear shocks as well as a Stanza front end it is a very adequate combination and improves handling greatly.
I am only now having a few engine problems from continually driving at high revs and with about 1 litre of oil in the engine. Because I just bought an A15 motor (1500 Nissan Vanette) motor to replace the old A12 motor (1200 standard 12Y motor), I want to see if I can blow the old motor up and I can tell you that it's hard work even with nearly no oil left in the engine. I have been trying for a while and I have only been able to produce a bit of a bottom end bearing rattle, and a sufficiently smoky car, nothing else. The engine still wants to run forever (typical Datsun engine).
All Datsuns are great cars and I recommend them to anyone. I especially recommend 120Y to those people who are learning to drive and/or buying a first car. Because they are easy to get, cheap to run, buy and repair, they are not very powerful so you learn to make the most of what you have, and they have relatively good handling (depends on how well it has been maintained).
I am currently in the process of severely modifying most aspects of my 120Y. In the future I am hoping to modify my car more apart from the 1500 engine and the Stanza suspension. Some of the things I am hoping to do are fit a Toyota Celica 5 speed manual gearbox, a Nissan/Datsun Bluebird limited slip differential (which has to be customised to fit), a Holden Gemini radiator and a thermo fan.