Aviatik,
Dispatch reliability, as you will appreciate, depends on good maintenance in the first place; even a new a/c will soon go AOG if not cared for.
The DC10 has a solid airframe and (relatively) uncomplicated systems, usually in triplicate . Provided your particular a/c has a "good" history, and your company is prepared to give it some TLC on its maintenance downtime, the reliability should be no worse than the twins.
Spares are expensive...a few operators have bought most of the world's stock, so parts are available but at a price. Consider this scenario :
The maintenance organisation is unwilling to pay the quoted price & hopes to find a cheaper part elsewhere. This takes time. Meanwhile the a/c is operating a week or more in accordance with the MEL with (typically) one system locked out,increasing the workload on the other 2 ; finally one of the remaining 2 systems might fail (this usually happens at the most remote airfield on the network). The resulting AOG costs many times the price of the spare originally required!
The MEL was never intended to permit continuous day-to-day operation on 2 of 3 systems, which short-sighted companies today increasingly believe they can get away with, and so IMHO this is not the aircraft's fault!
I've been on the '10 for many years and I still love it...Enjoy a real pilot's classic!
DCD