Hi,
Lucas oil is probably not a good thing for the gearbox. The notchiness in the Getrags is pretty typical so your best bet is to use an oil that behaves the same hot or cold. Of course, you would want it to act like it is warm, at all times.
Redline Oil makes a synthetic ATF which is called D4ATF, I believe. It is excellent for the Getrags (I used it in my 535i for years) and it addresses the notchiness. Another good product is Swepco, which comes standard with some Porche models. I have used it too and it works very well.
Hope that helps.
Regards,
Adnan