New release bearing? How is your clutch cable adjusted? Have you allowed a little bit of slack in the fork?
Can't say much about the whine in first gear other than, why are you decelerating in first gear? First gear is just to get the car moving so you can use 2nd as soon as possible. Wouldn't decelerate in first ever really.
I'd look to see your clutch cable adjustment incase the release bearing is up against the clutch plate constantly. Then remove the box and see if you need a new release bearing before rebuilding the gearbox?
Would help if you had a video of the noise?
Oil definitely in the gearbox?
Adrian