I had a 1992 C7 topkick with a 55ft Holan Bronco boom, boom was actually in great shape, but overall a money pit, cost me 70 grand in downtime in a single year
only buy a bucket if you can afford for it to sit frequently while its being repaired, rotation bearing requires a crane, and removing the entire boom, outrigger cylinders require a backhoe or a LOT of manual labor to remove, I've done multiple, it sucks, especially if pins are seized, boom hoses are around 55 feet long unless they split at the knuckle, you are looking at over a grand a hose, depending on the boom you may have 10 or so that have to be replaced every 5-8 years, don't forget insurance
at 17K hours, I would steer FAR away, transmission will be due for a rebuild, PTO has high hours most likely, engine needs replaced or rebuilt, hydraulics likely need flushed, etc
even if it currently works every day, to have everything up to date (unless the seller has paperwork to prove repairs or maintenance, assume they were never done) you are looking at anywhere from 5 to 30 grand
now, that being said, I've operated high hour equipment that ran like it just left the factory, so theres a slim chance that its a unicorn, worth checking out but look it over with a fine tooth comb