So if the joints seem good and the boots are starting to look old and cracked, you might want to replace clean and repack the joints and put new boots on.
The rule of thumb, as I learned when I was a Nissan dealership technician, is that if the boot is split, but the CV's not clicking loud, shoot some more lithium grease in there and install a new boot. If it is clicking loud, take it to a CV rebuilder. Yes, you can rebuild it yourself, but I'd only give it a 10/10 guarantee - 10 feet or 10 minutes, whichever comes first.
if you lose the timing belt you are screwed. If you lose the water pump, it will probably take out the timing belt and your screwed again.
The timing belt is a 4 hour job if you do all the related work and you have an idea what you're doing. Take the cover off and evaluate the situation. There are 5 things to look at.
1) Timing belt. No missing teeth, no teeth peeling away, no fraying, no cracking. The 300ZX belt is plenty strong when it has less than a gazillion miles on it, but if you feel froggy, swap on a set of cam and crank pulleys from a Quest and use the Quest belt - it's beefier.
2) Water pump. There's a weep hole on the underside. If it ain't weepin' you should be okay, but you might take a spare just in case - 'cause it does suffer the curse of the Z.
3) Welsh plug. It's the plug in the coolant passage that's seeping coolant. YOU WILL NEED THE SNAP-ON SOCKET TO GET THE PLUG OUT INTACT. If you can't afford to buy the socket, you might try finding a bolt head that fits snugly in the hole, put some nuts on the bolt, and try to remove it that way, but it takes a buttload of torque to get it loose. Clean all the crud up, put some quality puckey on the threads, and re-install.
4) Tensioner. If the bearing's rumbling, replace it. It it doesn't roll smooth, replace it. The timing belt, water pump, and tensioner all work together or your motor's toast.
5) Cam seals. If they're seeping, I wouldn't worry about it. If they're leaking bad, replace them. Hold the cam sprocket really still, unbolt the sprocket from the cam, and gently tap a screwdriver between the seal and the head so you can pry it out. Yes, you're putting a few mild gouges in the aluminum. You only screw up if you mar the cam or really gouge the seal mounting surface. Use a socket to lightly tap the new cam seal in place - I recommend installing it at a slightly different depth than the old seal just in case the old seal wore a groove on the cam.
When you install the new belt, you want to wiggle it and feel a little "snap" to it. It's really difficult to explain, but it's right on the fine line between being too loose and being too tight.
If you have the budget for it, replace your gear oil with Redline Synthetic. That'll help your tranny and rearend durability.
Also, Nissan had a recall in the late '90s to replace the injector hoses on the VGs. It's about time to do that again. Make sure you get good quality hose - Nissan had to recall them because the VGs kept turning into roaming barbeques.
Good rear shocks are a necessity on IRS cars. I know the Zs tend to jump on upshift if the rears are shot.
