I have a 20 year old Nag gas Ducane. Up till now I have never had to replace anything on it. It does need a new burner tube finally on the left side and the ceramic briquette tray is starting to burn thru in a couple of places.
I have two half barrels and three grates for any charcoal cooking we do. We usually do 50-60 chicken halves a couple times per year for parties at the house.
We normally grill 2-4x per week 8 months out of the year and 1-2x per year the other 4. I've been pretty happy with it and the price was budget friendly as well for a large grill. Two of the spark igniters did break after a couple years (the ceramic portion that holds the spark wire cracked and broke apart when I brushed them during a deep cleaning). I still need to get them replaced, but other than that and a couple screws that have corroded and broke on the interior, we've used the heck out of this this grill for the last 3 years and it's been a rock solid performer otherwise.
The stainless grill plates and interior are in great shape still which I am pleased about as my last grill was a cheap big box store grill that did not hold up well.