Well I was concerned when we first got ours as you. There is a engine manual , a transmission manual , and info on the chassis manufacturer. On the engine there is a warranty ( Cummins is 5yrs or 100,000 miles). Allison is 3 years or 50,000 miles I believe, and 3 years or 50,000 with Freightliner chassis components ( includes transmission ).
Many parts are covered if they are due to a break down " providing" the required maintenance is done. That means oil changes, coolant flushes, transmission fluid and filter changes, etc.
I Just sat here on vacation reading the manuals for required maintenance. Oil changes are due yearly on both engine and generator with all filters ( already done ours). So for me, it's a no brainer to have the rigs oils changed yearly, and a real piece of mind it's done.
Coolant according to Cummins should be flushed at 2 years. Transmission flushed at 1 year and then extended fluid can be added to allow for 3 year intervals.
I've put together a list of maintenance items needed to be done. I will be letting Cummins and Frieghtliner do the maintenance, but directing when it needs to be done. That is your responsibility to decide what is important to you and if you want to keep whatever warranties you have valid.
Reading all the manuals is a task but should be done. There are things you can do yourself like pulling the air tank lanyards every 6 months. Checking drive belts, checking oil levels, coolant levels, proper air system operation, looking visually for leaks, checking tire pressures before trips, etc.
If you put together a plan on paper ( or i-pad like me) to keep on top of the main items it makes it easier then pulling all the manuals out every time you need to look. Hope that helps.