Welcome to our world where oil changes and routine chassis service costs hundreds of dollars
. Be prepared to spend more time and money while you get the Horizon shipshape. Call the Freightliner dealer that said you had bad 'bushings' and ask exactly what they are referring to.
Servicing a heavy chassis like you have is more difficult than working on a car. The engine probably uses 20-25 quarts of oil. the axles probably have 20 quarts of gear oil, there's an air dryer with replaceable element to keep the air moisture free for the brakes, the transmission is most likely an Allison 3000 which uses ~20 quarts of fluid, the air cleaner is the size of a small trash can, etc.
Since you have no maintenance records, assume
all routine maintenance needs to be performed - this means a complete chassis service with all filters and fluids replaced. If the Allison transmission fluid hasn't been changed to a synthetic fluid, you should have that done as well.
Your air bags (if not previously replaced) might be cracked and need replacing (there are four of them.) You can get a good idea of the integrity of the air system by seeing how long it takes your air pressure to leak down after shutting the engine off. A fully 'tight' air system will retain air pressure over 100 pounds (or so) for a day or two.
Couple of tips.... If possible, use a
Freightliner Oasis dealer for your chassis service. They are identified as being 'motorhome friendly' - in other words, they are used to servicing motorhomes and not just heavy trucks like a non-Oasis dealer.
Join the
Freightliner Owner's Chassis Club and receive 10% off parts when serviced by a Freightliner dealer.
Here's some maintenance tips from Freightliner and
here's the 'bible' of service required at mileage intervals.