First call; if on road side ; would be GS , when I lost hydraulic pump drive , GS got a tow truck , located a safe spot to park the coach ( closest Freightliner was closed on the Sunday so they couldn't confirm them as an RV repair facility ) they found a mobile mechanic , and when the issue proved to be beyond mobile repair , sent the tow truck again; next morning; to move the coach to the dealer.
Now if you have a break down at home , and feel you're capable of a DIY , then Freightliner or Cummins would be the first calls.
NOTE: as Freightliner discontinues support of older chassis ( 20 + years ) then , F/L is less of the option .
JMHO: Call Freightliner now, with your serial number , get wiring diagrams , wiring schematics , air system diagrams , JOIN DTNA Connect , and get access to part numbers for items linked to your chassis serial number and keep comprehensive notes , for your future use, and to pass along with the RV if/when you sell , sooner or later those notes & info, will come in handy .