Yeah. Pretty sure you can do that. Its possible to actually change gear without the clutch when driving, but you have to do it very slowly and its not particularly advisable.
Silkolene in gearboxes is crap.
The notchiness of the 6MT is reduced quite a bit by overfilling the box with to about 2-2.1 litres. This obviously has to be done from the top, and its advisable to extend the breather slightly.
I think the price for a new box from Japan was quoted to you on an SXOC thread. Its not going to get cheaper. My suggestion was to replace any internal parts if there was a problem. You don't need an account with Perfectrun. You just email them with the part number(s) and ask for a price. They'll email you back and then you order via their web site. Once sent, EMS takes about 4 days. Labelling the parcel a certain way reduces the risk of it being stopped in customs
It should be a case of parts being with you within two weeks of first emailing PR. Considerably quicker and cheaper than trying to get them from Nissan GB...
I couldn't really say for sure what the problem is. Even if I drove it, I wouldn't be sure, though I could probably tell if it was the clutch/fly.