Preventive maintenance is the process of checking, adjusting and renewing components BEFORE they break or wear out.
The TMs for vehicles of the M44/M35 era were written with two major thoughts in mind; maintaining the vehicle so as to be able to operate it in an austere environment fo 60-90 days with a minimum of major breakdowns or time consuming repairs and, second. an assumption that the PMCS would actually get done "by the numbers"
As such many check, services and parts replacements were specified at time intervals and wear limits that are much more conservative than most of us need to do.
Since few if any of us have the resources, including time as a resource, to follow the GI PMCS and scheduled maintenance regimes we have to determine for ourselves which to do and when.
With a well thought out maintenance program that reflects our own use, budget and tolerance level for surprises, any of these trucks can be kept reliably running for a long time.
Mechanical equipment (trucks, tractors, old engines) that sits around and only get occasional use has problems and stresses different from equipment that gets frequent use. Often things like seals that lose resiliency due to non-use, internal corrosion due to condensation, fuel and lubrication systems gumming up from non-use etc cause the premature failure of components and lead to low mileage replacement.
Driving it once a week, even if only a dozen miles will do wonders for the truck's longevity and durability. It will keep all the seals pliable, keep the fuel system flushed, dry the condensation out of the engine, exhaust, transmission, transfer and axles, keep the batteries healthy etc.
Another important consideration would be that in seeing and operating the vehicle often it is that it is much more likely that you'll spot, hear, smell or feel a problem while dealing with it is only important and before it becomes urgent.
Lance