As has been pointed out TOS made very little use of technobabble, it being a product of later versions of Trek. In his autobiography James Doohan claims he argued against Scotty's use of technobabble in 'Relics', on the grounds that neither Scotty nor real life engineers talked like that. He was told that Rick Berman likes it, and that was the final word.
So to capture the TOS style, keep it short and simple: "Aye, I said an hour, but I thought the conduit had just burnt out. Turns out it'd overloaded, fusing the distributor entirely. Whole thing's got to be hauled out an' replaced. That's a six to eight hour job to begin with, an' it' take just as long to bring it up to operatin' temperature. An' that's if we rush things, an there's no delays. I'm sorry Mister Spock, but I just canna do it faster than that."