Gear Selector Problem

Guys I am after some help with a problem that I have on the girl friends 98 E36 318is manual. The gear selector is very stiff to push toward the left as you put it in reverse and also fairly stiff as you push it to the right as you put it into 5th. It operates normally when you only use 1st, 2nd, 3rd and 4th.

I'm in the middle of a clutch change so I have the gearbox out and will be changing the oil, and Im also rebuilding the gear selector linkage. It has a bit of a selector shaft seal leak so I will replace that.

Do you think an oil change will help the problem? Or is there some sort of mechanism inside the box that acts as a return spring for the extreme left and right travel of the selector that could be 'sticky'?

Thanks heaps, Myles