Hey Glenn - good to see you again!
With the relatively low sales number on the F50 series, we don't have as much experience to draw on - but we're seeing a decent trickle of posts now.
I'd think needing shock replacement is a real possibility, but it may not be necessary yet... my wife's '04 G35 with 122K still seems pretty good.
There are several online parts places... my latest is
http://www.orderinfinitiparts.com - but I'm not totally in love with them either. Their big advantage for me is that they're in Charlotte, NC - so FedEx ground arrives the next day if my order is in stock. The old days of calling up a TJ or Joe and ordering parts on the phone appear to be pretty much over. Apparently the parts business is so cut-throat that live customer service is an expense that can't be covered by the places offering a discount. I've found that going to Infiniti's site and looking up parts is like having a copy of FAST in the old days. It makes ordering a little easier online.
Here's a thread about a problem with the sport suspension that developed shortly after shock replacement.
2003-q45-sport-suspension-not-working-t589460.html
ATF should be replaceable. Check out the FSM at
http://www.infinitiservicemanual.com - the FSM for our G actually recommends a flush that involves pouring fluid in through the filler tube, while pumping it out of one of the cooler lines - which was always considered to be a bad idea on the older Q. I'm assuming the fluid is routed differently in the more modern transmissions, and fluid starvation isn't a concern?
I haven't heard of exhaust manifold cracking...
We've seen a couple of display failures... I think there's a fluorescent tube in the dash that fails. There's also an issue with the "joystick" that fails on the dash. If I remember right, there are some aftermarket repair services.
Bose seems to be pretty solid based on not hearing much about issues with it.
I'm not sure if the oil consumption gets worse on the engines that started out with it... you already know this, but I'd certainly have a dealership pull the history by VIN and see what was done on it...
Sadly, the quality of the F50 isn't that of the older Q's... that said, I don't know that you're going to find anything like the G50 in a modern car. I have no idea what I would buy if I had to get something today. The wife's G has been a real disappointment in terms of paint quality - but it's been rock solid mechanically - so I can't complain too much. Other than fluid maintenance and tires - all I've had to do to it is replace the driver's side seat track, one front wheel bearing, and now a leaky radiator that I'll be replacing this weekend.
Heath