Questions, gearbox, mounts, engine Options

[Euphoria]

Hey, lately Ive been unlucky and been struck with a few problems.

My rear main oil seal started leaking and now my 3rd gear has started to grind ocastionly, my questions are what is the problem with my 3rd gear, If I double clutch it still grinds and if I rev down it still grinds a little, and it only ever happens every once in a while, other than that its perfect, the grind also sounds like its coming directly under the gearstick, does this mean its not my syncros and my gearbox is slowly dying? is it normal for the sound to come from here? and is it possible its my motor mounts?

I've also noticed as of late that I have to rev a bit harder to take off than I used to and if I don't the car vibrates, by this I mean I have to take off at 2000rpm and ride the clutch which I can't remember doing before, could this be the rear main oil seal is leaking onto the clutch possibly?

Another issue is that the car doesn't seem to always rev smoothly through the revs, some days it will go all the way up and be super smooth and other days it will be rough, Ive stayed using premium fuel and it hasn't changed how smooth it is, I also did change the oil to 20-60 pennzoil semi-synthetic, to calm the leak down and that it has, could this be causing it not to be as smooth?

thanks heaps.