I have a 1989 MCI 96A3, same bus 6 inches narrower.
Check all the fluids, the 8V92 engine uses a special oil, straight 40 w CF2 low ash, Delo 100 is a good choice and available at Orielys, most Detroit 2 strokes will leak some oil and you will need to check it and add occasionally.
The engine oil dipstick will be on the lower curb side of the engine when looking at the engine from the back of the bus.
Check the Transmission fluid, dip stick will be on the driver’s side access hatch in front of the air cleaner, check to see if it is full and clean.
Check the power steering fluid, there should be a sight glass on the curbside of the engine looking straight into the engine compartment past the engine from the back of the bus.
Check the oil level in the blower drive at the top of the giant fan belt, there will be a sight glass.
Check the condition and tightness of the fan belt, if the original piston is still there it will tighten up as the air pressure builds.
Above the blower drive on the tank there should be a sight glass for the coolant level.
If possible get an oil sample and have it analyzed, this will give a good indication to the health of the engine.
65,000 is nothing for a Detroit, watch the exhaust when starting see how long it takes the smoke to clear, a small amount that clears quickly could be ok, thick smoke that takes a while to clear could mean expensive issues.
If you are not familiar with the Detroit 8V92TA it is different from any engine you have dealt with before, it is a two stroke, with a blower pressurizing the intake and a turbo feeding the blower. A very dependable engine when running good, but expensive to fix when it breaks, they have been out of production for a number of years and good mechanics that understand them are getting hard to find, none the less these are good engines with a loyal following, if you are able to do your own work a lot of help can be found on the net, check out the Bus conversion Magazine forum, https://www.busconversionmagazine.com/bcm-forum/
How long does it take the air pressure to build? You need at least 100 psi to move the bus, 120 psi is good, listen for air leaks, unless they have been meticulously maintained they all will leak air, The air powers the brakes and the suspension, so big air leaks are bad.
Check all the air suspension Bags, one on each side front, two for each side drive axle one for each side tag axle, look for air leaks and dry rot, they are not terribly expensive (Relatively speaking, everything on a bus is expensive) or that difficult to replace, but something to consider.
Check the tires for tread and age anything older than 8 years is suspect, figure around $500 per tire to replace.
Tire pressure should be 90 to 100 PSI.
Examine all the lugnuts, they are torqued to 450 Lbs, most have been abused, not expensive but a lot of work to replace, drivers side lugnuts are left-hand threads.
Check all the Hubs on the steer and tag axles there will be a cap in the center there should be a visible amount of oil in them, if it is low suspect the wheel seals to need replacing and the bearings to need inspection and/or replacement, if the wheel seals are bad then there will probably be oil on the brake shoes as well.
If you can get under to check the brakes, the shoes should be visible in the drums, look to see if the shoes are worn past the line in the middle, look to see if there is a visible space between the drum and the shoe, the slack adjusters might (probably) need to be adjusted, look to see if the wheel seals are bad and the shoes are oil soaked.
A word of warning here, be sure not to get under this bus while it is just being held up by the air suspension or just a jack, this thing weighs 13 tons, if it comes down on you, you are dead.
These are some of the things to check to possibly make a safe ride home, there are many more things that will need to be serviced if you buy it.
My Bus was fresh out service and it had not been maintained very well for at least 10 years and there were some very shady things done that were not visible on a quick inspection, so beware.
Feel free to ask any questions.