Quick background: I'm a farmer / propane truck driver/ firefighter / retired volunteer Fire Chief.  I'm really having trouble responding because I've been on so many sides of these issues. Mikado I fully understand wanting to have well working equipment but not wanting to spend money needlessly.  Keep one thing in mind.  When you add the word "fire" to a piece of equipment (any equipment, even a hammer) the price doubles.

Oh, and folks keep this fact in mind:  How fire departments are funded and operated varies widely hugely in this country.  Mikado mentioned his district serves  "4 municipalities. 2 villages, 2 townships" and it appears each entity has a finger in the pie of funding it.   Other places volunteer departments are donation funded, subscribed to, fully independent taxing districts, municipality owned, on and on.  This isn't necessarily part of equipment cost but it is a big factor on how things are done.  What my dept. does and how yours does it may be quite different.

Let's side step truck and start with tires.  There is a manufactured date on tires.  (If not they are too old and need replaced).  Regulations say tires must be replaced after ... I forget if it's 7 or 10 years.  7 I think.  Do you know how hard it is for a farmer to discard good looking tires regardless of the age?  We were discussing tires on our fire trucks last year.  All were at least 20 years old.  Trustees agreed we should probably put new steer tires on but the rears were still OK.  Before we got around to it I (fortunately me the old truck driver and not one of the inexperienced young guys) was driving our pumper on a training night run when a steer tire blew. Blew as in busted the fender and headlight and made 2 grooves down the blacktop.  We bought one new tire that night and 11 more in a short period of time.  I've been looking closer at my farm truck tires recently.

Fire trucks is a complicated subject.  They are way too expensive to buy and maintenance is unreal.  Remember I said add fire and the price doubles?  That's a conservative estimate.  One of the difficulties is what we need in rural SE IL probably won't be the best choice for most cities.  And probably not the best for rural South Carolina or SW Wisconsin.  And the rules and regs are made by folks sitting behind a desk in a metropolitan area with a union lobbyist and a truck manufacturer buying them coffee. (that's going to get me in so much trouble)

Our pumper was a 1996 IH that a company in Alabama made.  They took used chassis (I think ours was a Penske or similar) and put new apparatus on them  So our equipment was 5+ years newer than the truck it was on.  Great idea for smaller depts.  They're out of business.

Anyway, about 5 years ago we were having an engine issue and I (Chief at the time) ended up taking it to an IH truck dealer.  The parts guy kept going on about how old it was and he wasn't sure if parts would be available.  I looked him in the eye and said "Son, that's our newest truck."  That's the chassis.  Same thing applies to 25 year old fire apparatus parts.

Our 1986 Dodge brush truck had under 10,000 miles on it. It was on its third set of tires and third carburetor.  They dry rotted sitting in the station.  Good old truck other than it had a manual transmission.  We had 2 firefighters that could not drive a stick.   A door latch failed.  The part was NLA (no longer available).  I found one at a salvage yard.  Windshield wipers quit.  The "towers" the wiper arm pivots on were froze up.  That part is NLA.  I was able to take the whole assembly off and at the farm shop heat and beat until we got it working.  We replaced it with a 2006 another dept was replacing.  So to the comment "doesn’t matter if they have a close to 30 yr old truck or brand new truck" Yes, it does matter.

Oh and someone mentioned ISO (the insurance rating folks).  A brush truck does nothing to help your ISO rating.  And a 30 year old fire truck does affect it ... negatively.

I've written a book and still haven't got to the main point.  I'll try to come back later and get back on topic