Don't be sorry for asking this question. $20,000 is a very large investment for most of us, and you should be sure it is what you want.
I am one of the members who frequently has had quality and gear problems with my Si, but I have to say something:
Whenever you log onto a car forum, you are going to get two extremes: the best of the car and the worst of the car. You are going to hear about how much people love their car and that they have no problems with it, and then you are going to hear people who love their car, but have had numerous problems with it. While every car has its set of problems, going to a G35 forum is going to net you the same kinds of extremes.
For me, personally, I am not a hardcore driver. I don't rev up to 8K RPM in residential or stoplight traffic. I very rarely open it up at all unless I am passing someone or merging on a freeway. My car is a daily driver that doubles as a weekend car. I can deal with the rattles (which are abundant), despite being disapopinted in the quality control for this car, the crappy paint (which is frequent among a lot of cars anymore), and even the wear-prone and scratch-prone interior. However, this third gear issue concerns me.
I do not know much about transmissions, nor do I pretend to. I have switched my MTF to the new Honda fluid, which hasn't helped all that much (most members switch to Amsoil for the best results). I am concerned that down the road, these cars are going to exhibit some kind of problems with the transmission because of damage the grinding and popping out may have caused. Again, this is just my speculation and concern, I have no idea. For me, this car was supposed to last me through college, into grad school, and even the first few years of my career, however I am starting to question whether it is able to do that. I love the sportiness, but the long-term quality of materials and the transmission is over concern to me, not so much the engine.
What you need to do is decide whether you want to live with a problem Honda is probably never going to address. You may not even haev it on your Si, as some members have not had any grinds/popping from it. If you do, switch to Amsoil for a bandaid to it, which is your safest bet.
If this is something you can't live with, look at another car.
I hope this helps

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