I think it depends on the part. I recently purchased a new harmonic balancer for a 292 from Tom Lowe over at 12bolt.com. Tom sells what I consider to be excellent parts. One reason, he actually inspects them and many times makes them better quality then when he received them. Case in point. My balancer was not only inspected by Tom, but Tom balanced it in-house. I purchased a machined crankshaft from him for a 292. Fully machined and balanced in house, everything checks and correct.
But then, you have the opposite. Off-shore parts, low quality control at the manufacturer level, poor metallurgy, poor machine work, poor to no quality control at the distribution level. Jon (carbking) has detailed some of what he has found in the new carbs being sold. Lifters, oh don't get me started.
I just recently rebuilt a vent window. New rubber, new whiskers, new glass, new hardware. Cleaned, painted. installed the unit and used the "reproduction" adjuster for the bottom the the vertical track. The threads were not cut right and the nut would not install properly jamming the adjuster up. I actually threw it across my garage, went and got a crusty, rusty original, re-habbed the original, and installed it. Perfect.
I thought to myself, heaven almighty, can we ever get a new part that does not have to be modified, altered, adjusted, fiddled with , ground on, or totally redone just to have it actually work the way its supposed to.
