Variations of GS6-17BG Gearbox

Hi folks,



Abit of a newb here but I'm really stuck.



My E91 318i (don't laugh big engine folks!) has a tempremental gearbox where very occasionally, the 1st gear slips out of gear only when reaching biting point.



Speaking to my BMW independent, he recommended I eliminate the Clutch and Flywheel, which I had replaced this week, but still no joy.



So it looks like an expensive gearbox replacement for me, but the problem is that there seem to be many variations of it.



If I search on realOEM.com, I am told from a top level that it is a GS6-17BG (which I understand various other Bima's use), but if I drill down to the component it says I have a GS6-17BG-TPAZ



But looking on Ebay etc, there seems to be other variations.. such as GS6-17BG-TCAA or GS6-17BG-TCAQ



I'm trying to find if these last four digits actually matter or not ?



Could anyone help ?



Also, would you trust