I can say this. If you have a talented and caring in-house shop with a set-in-stone preventative maintenance program...and they are not beat to h### on the "mean" streets...Seagraves should easily be able to run the 25 year NFPA service life and even longer. LA City sees plenty of fire duty and theirs lasted forever, before they switched (low bid...I assume). I understand FDNY is a different animal, but they are the exception. We still have a 1992 model in frontline service, making well over 1,000 runs a year...and when its replaced next year, I bet it runs as a reserve up to and maybe past 35 years old. Just saying... But, I'll admit this...with all the new crap required in engines and forced on us by the NFPA...it will definitely be harder to get a new rig to last that long from here out.
EPA is certainly the engine stuff. Without starting WWIII, by NFPA, I meant all the other stuff (most of which truthfully is meant to improve safety) that end up being the gremlins that plague some newer apparatus.
Just throwing my two cents in - the NFPA is not a regulatory agency. They are merely making recommendations. Now, "most" agencies try to follow those recommendations, but are not held to following them strictly.
Remember, it's their Emergency, not yours ! Arrive Alive !