Should I buy a motorhome that has been sitting for six years?

It is a Ford 460 V8 which has idled often while parked at a lake but unit has not been moved in six years. Should I be worried about anything? Differential, transmission, driveshaft?

If you plan to drive it I'd worry a lot about the tires first. Then I'd worry about other things.

Dummy, when buying anything vehicular related, you get it checked by a mechanic. Things like a drivetrain don't deteriorate by not being used, unless they are exposed to harsh environmental conditions and corrosion. Start it up, check fluid levels and look for drip spots. Drive it to a mechanic.

How old is the unit? How many miles? Whst was the upkeep and maintenance?

Just about everything needs inspection and there will almost certainly be many problems other than the engine. For example - suspension, brakes, coolant system, bushings.

Not a good idea. All fluids would have to be changed. Tires might have to be replaced. Have a mechanic inspect it first.

The tires may have taken a "set"and have a flat spot on them.

First thing I'd look at is the brake system. The hydraulic lines are probably all rusted into submission, and calipers and wheel cylinders are frozen up. Next is rotors and drums are rusty done. Pads and shoes, AND HARDWARE! Check the rubber flex hoses also, may be dry rotted and cracked.

THEN, you can check out the rest of the unit. Inspect and replace ANYTHING rubber, such as fuel, power steering, and coolant hoses. New tires are probable.

Certainly, all fluid changes, coolant, oil, trans fluid, power steering fluid, rear diff oil, etc…

Getting the feeling, buying a long sitting vehicle gets expensive?

And we haven't even talked about starting/ charging/ electrical/ chassis/ drivetrain systems yet…

NOT WITHOUT A MECHANIC CHECKING IT OUT FIRST!

Unless you are getting it dirt cheap, no. Figure every bit of rubber on it is dry rotted. That includes the tires. Look up the brand and check out how they mark the date of manufacture. You probable will find the tires are at least six years old, maybe older. They need to be replaced and that is going to cost at least $150 each tire. I bet it has at least six of them. All the belts on the engine need replacing. You will need to put in new oil, transmission fluid and radiator fluid. The air conditioner unit/s are probably shot, figure $1000 to replace one. The fridge is probably shot too, figure another $1000 for that. If it has been parked at a lake and they did not take pest control precautions then mice may have gotten in and left mouse poop all over (look up Honta Virus.) They could have chewed out wiring too. You may have a beehive or wasp nest somewhere. The batteries all need to be replaced. (One engine battery, four 6 volt coach batteries or a single big RV battery.) That is another $500 if you go with regular lead acid batteries. The water system has not be purified in years, you will have to do that. The seals on the sewer line and gray water lines are probably rotted, you will have to replace those too. Lastly, the body has been taking a beating for years, parked outside. You may need some major roof and fiberglass repair.

Will depend on price and condition versus outlay getting it back up to scratch. Will need full service and if not moved in that time may even need towing or lorry lift and transport? Assume nearly everything will need replacing or referring. Interior may be Ok.
a good mechanics report is a wise investment. As potentially we face possible renewal all fluids. Tires. Hoses. Drive belts. And other issues will no doubt come to fore.
if still interested in facing some expense and work. Get mechanic in first. He may? Even be able to assess for value. Better to be a few bucks out of pocket on a report than hundreds times more on buying a lemon.
it may even be if well cared for but simply not moved? Need things such as brakes .tires etc sorting. Chassis check essential!

V8 which has idled often while parked at a lake but unit has not been moved in six years. Should I be worried about anything? Differential, transmission, driveshaft?

Look at this logically. The engine ran often(meaning it is the parts that get worn out because they are moving… The reason the engine ran is to charge the batteries and to supply heat inside the unit from the hot engine in the winter.

Parts that don't move might as well be wrapped up in plastic and put back on the store shelf as they are still new. The diff., trans, driveshaft, brakes are not used at all. That also goes for wheel bearings.
The tires would over time develop a flat spot on the tire. No big deal as they normally go round again when driven on the road as the next time it is parked the chances of it landing on exactly the same spot on all 4 wheels is 1 in a trillion. Tires would normally get sun baked and just dry up and crack on the outside after 5 years, so that would normally have been changed before then because the motorhome is meant to TRAVEL, so miles get put on it. If it has leaf springs, they MAY have sagged and maybe not. Shocks also should be good and so should radiator and water pump. Probably will have more problems with pack-rats making a home there or spider webs underneath than anything else.

The rest of it, it is a 6 year old motorhome, so plastic seals may crack like around windows, and the plastic stuff inside just deteriorates due to age. It is what you see.
Engine wear would not be excessive as even idling is not like driving for days and days at highway speeds at a higher RPM

What you see, is what you get. Obviously, it has been Lived in during the summer months.

Other than that, it is the AGE of the vehicle. The number. If it was never lived in and just sat at the back of the sales lot… Then it is basically a NEW vehicle made 6 years ago and never sold.