Sticky 1st gear. Which oil??

Hi, I'm going to drop and replace the gearbox oil on my wifes 2006 Passat 2.0 tdi but unsure as to what oil is recommended. When cold it really stick coming out of 1st gear and I'm pretty confident some fresh oil will cure it. Any suggestions as to which oil to use?

Which Transmission? Auto or manual?

Its manual. I've just ordered comma 75w90 fully synthetic GL4 after phoning local vw garage.