yes it is,but sometimes it is not impossible to do a visual inspection if you do the right diagnostics,i agree with the servetic mechanic that it is imposible to visually inspect without tearing down the trans,but did they tell (like what speedyfix said) that they performed visual inspection for clutch master and slave cylinder fluid leaks (for hydrolic controlled)or did they perform visual inspection for any sign of worn,stretch or damage cable? (for cable controlled)and did they perform clutch pedal play check?did they tell you that they performed all of this?if they did and all of them are good, then have a second opinion,drive your car to another shop just to see if they have the same result before jumping up to that conclussion (trans teardown).to those who have shop,pls.guys no offense.