I have a 2005 VW Jetta 2.5L (MK5, 5-speed manual) and the clutch grinds when I shift into first if I don't depress the clutch pedal for about a second or two first. One thing to note is that before I purchased the car, the previous owner had a single-mass flywheel installed, replacing the OEM dual-mass flywheel. I believe they also replaced the clutch.
If I just press the clutch and immediately shift into first it will grind and then go into gear.
If I press the clutch for a second or two, then it shifts into first with no issues.
So from doing some research, my initial assumption is that there may be air in the clutch hydraulic system, or the pedal-to-master cylinder adjustment is incorrect.
Any other suggestions? How would I verify which is the issue?