I have had my 1.8t since new in 1998. Even back then the gearbox was a bit notchy going from first to second. Worse when cold. In fact it was the only disappointing thing about the car. Fast forward to the middle of last year and I noticed an oil leak from the oil seal where the driveshaft enters the box. I used a local transmission specialist who did a very good job. As the car had done over 100,000 miles I asked for a gearbox oil change. They used a Castrol oil spec that matched my Haynes manual.
Afterwards I started to notice that it was very difficult to go from first to second or third to second or even engage first gear unless totally stationary. However, all seemed OK when the car had warmed up thoroughly. Internet research pointed to the oil that had been added.
So as part of a oil change service at a VW main dealer I asked for a gearbox oil change with genuine VW oil. Interestingly they could not give me a price straight away as it is not normally done.
It really seems to have done the trick. It took a few miles for the new oil to fully circulate and disperse the remaining Castrol oil from the components but I could even say that the gear change is now better than new and the car is at 113,000 miles.
As a word of caution, the VW mechanic either cross threaded or over tightened the engine sump plug stripping the thread when changing the engine oil. They admitted it straight away and paid for a new sump pan. I took the opportunity to pay for a new oil pick up pipe. Peace of mind really as there was no blockage but it shows the benefit from using fully synthetic longlife oil for the total life of the car.