D17 are good little tractors, I still own one and my family still has a D19 and a WD.
I have split D17’s, over-hauled the engines and rebuilt both the Power director clutch and the plunger pump.
Normally a properly functioning Power Director clutch will not cause a noticeable heavy load on the engine.
From the original description you gave it sounded like a miss adjusted power director clutch or has one post said it could also be a warped plate.
But… If you’re satisfied with the condition of the tractor then it comes down to price. After-all you’re the man buying the tractor and its hard to diagnosis a problem setting at a key board.
D17’s are very unique in the fact that a kit used to be available that allowed a 2 or 3 spool hydraulic valve to be plumbed into the circuit of the plunger pump very similar to that of a D19. (Most people don’t know this fact)
The only draw back to the kits was the lever had to be in the raise position to make the hydraulic valve function and you would lose the tractors Traction boost feature.