My '85 SD has the original motor and tranny and they have never been rebuilt. My bro-in-law used to own a '82 SD and he beat the hell out of the thing and hardly ever did any maint. (50,000 between valve adjust, tranny slam to chirp tires, etc.) When he sold it, it was hard to start but once running it ran fine. It had 440,000 miles. The only thing that was replaced was the turbo.

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'85 300SD (formerly california emissions)
'08 Chevy Tahoe
'93 Ducati 900 SS
'79 Kawasaki KZ 650
'86 Kawasaki KX 250
'88 Kawasaki KDX200
'71 Hodaka Ace 100
'72 Triumph T100R