1997 Honda Civic Loud grinding noises

I recently purchased a 1997 Honda Civic LX with the 1.6L engine and manual transmission. Since the purchase, a loud grinding noise has become apparent. I have taken it to two different shops, and recieved 2 different answers on the required repair. One shop told me the throwout bearing was bad, meaning I need a new clutch, the other said it was my input shaft bearing, meaning I needed a new transmission. Here is what I know about the problem.

- Clutch engaged (out) and not moving, no noise.
- Clutch engaged (out) and moving in all gears but reverse, loud grinding sound.
- Clutch disengaged (depressed) and moving (coasting) no noise
- Clutch disengaged (depressed) and stopped, only a slight grind when cold, none when warmed up. The noise on startup with a disengaged clutch is fairly new, about a week old.

I had the transmission serviced at an auto shop after reading a couple of forums. At this point I was told that the fluid smelled like gear oil, rather than Honda manual transmission fluid. It was suggested to me that I should use Mobil 1 synthetic 10w30, and so I authorized them to use it (apparently honda manual transmissions use motor oil). There was absolutely no change in the sound at all even after the fluid change, it is just as loud as it has been for the past couple of weeks.

The noise itself is a very loud grinding sound, almost like what you hear when a wheel bearing goes bad. I just want to clarify which component I should consider replacing. If it really is just the throwout bearing, a clutch is far less expensive than a new transmission and clutch. As far as shifting goes, it is smooth as silk, never hard to get into gear, and it doesnt pop out of gear.

Thank you for taking the time to read this, I hope to clarify this soon so I can resolve this issue.