Astra VXR M32 Gearbox Question

My VXR gearbox doesn't "feel" right and due to the fantastic reliability these have, I did some looking into the most common issues they have to see if this meant mine was on its way...
My car has (now) 16200 miles on the clock.
It feels like it grates/notches into 2nd gear. Not all the time though. Sometimes 3rd too. Thats on up shift. On down shift it sometimes struggles to go into 5th. Then feels like it grates/notches 3rd and 2nd. Again, it doesn't do it all the time. Also, although it feels this way on the gearshift, there is no noise from the box (as you would hear if it were actually grating the gears).
Just to note: there is no whining from the box, no funny noises, no play or movement in the gearshift whatsoever.
Anyone have any ideas? I was thinking of changing the gearbox fluid to a Millers 75/80 to see if this would improve the gear change but if it doesn't, I have wasted £40 on oil.
Thanks in advance.
Thanks Matt for all the info. So the feeling of it "grating" is the way the box is, not synchro's or something?
I drive the box "gently" as it were as I am worried if I quick shift it, it will grate.


Stupid Bollocks
thicker oil will make its notchy i put morris EP 80W-90 Gear Oil GL5 in mine and had a hard time getting 3/4
i changed it out for morris Lodexol SS 75W-90 and its better

you could also reset the selector to make sure the stick has the right movement to the gears
Thanks EvoCarlos.
Think I will order some decent oil from Opie and see how it goes from there.
How would I go about resetting the selector?
Can't get better than that.
Thanks everyone for the help. Am gonna try sort these items when I have the chance (which may take a few months!)