I have recently heard a noise in second gear ( windows down now). It sounds like a gear lash taking up but I don’t hear it that often. I first heard it after 3 laps of Watkins Glen but now hear it once in a while...not all the time. Any idea?

second question. I want to change the oil in the trans. Do I need to use the BMW special okl or can I use synchromech or 75-90 synthetic gear oil?

Gordon on has 90k miles on it.