Chris:
I have a 1984 Maxima, which I purchased used in 1991. I have replaced
portions of the exhaust system myself. When I checked the catalytic
converter (1995) it was, and still is in good condition. After 21 years
there is some rust on the exhaust pipe from the catalytic converter back,
appears concentrated on the welded seam, but is still sound. The only
problem with the exhaust system has been from the pipe traversing the rear
suspension to the tailpipe. I replaced these components for the second time
in September of this year. Weber remains one of the few suppliers of
components for the '84 Maxima. I prefer not to switch to a stainless steel
exhaust system, as this would just increase corrosion on the rest of the
car, by increasing the anode to cathode ratio.

Fitment is always an issue when purchasing aftermarket parts, domestic
tubing sizes are close to OEM but there are always production tolerances.
Be prepared to be have to modify the new parts to fit. Proper cleaning of
existing joints is essential in doing the job correctly - something most
muffler shops avoid by replacing the whole system - that way no time is
spent cleaning old parts -> time == money. Bandages for skinned knuckles,
and a blue language filter for the mouth (essential if the kids are around
while you're working on it). Be prepared to spend some time doing the work
right, because you aren't going to be able to do it in 20 minutes like a
muffler shop.
Best of luck
-bob

Chris:
I have a 1984 Maxima, which I purchased used in 1991. I have replaced
portions of the exhaust system myself. When I checked the catalytic
converter (1995) it was, and still is in good condition. After 21 years
there is some rust on the exhaust pipe from the catalytic converter back,
appears concentrated on the welded seam, but is still sound. The only
problem with the exhaust system has been from the pipe traversing the rear
suspension to the tailpipe. I replaced these components for the second time
in September of this year. Weber remains one of the few suppliers of
components for the '84 Maxima. I prefer not to switch to a stainless steel
exhaust system, as this would just increase corrosion on the rest of the
car, by increasing the anode to cathode ratio.

Fitment is always an issue when purchasing aftermarket parts, domestic
tubing sizes are close to OEM but there are always production tolerances.
Be prepared to be have to modify the new parts to fit. Proper cleaning of
existing joints is essential in doing the job correctly - something most
muffler shops avoid by replacing the whole system - that way no time is
spent cleaning old parts -> time == money. Bandages for skinned knuckles,
and a blue language filter for the mouth (essential if the kids are around
while you're working on it). Be prepared to spend some time doing the work
right, because you aren't going to be able to do it in 20 minutes like a
muffler shop.
Best of luck
-bob