E60 545i w/ 39800 miles.

Anyone w/ Manual Tranny ever experienced this?
First gear pops out during mild acceleration.

It's not all the time. I experienced this once when climbing hill (not step at all) and couple of times on the flat level surface over 3 month period.
I can't replicate it but one thing I know it happened during acceleration (not even a hard acceleration)

When it doesn't pop, 1st gear feels fine, no grinding, everything feels normal.
2-6 gears feel good as well.

Is this shifter bushing worn out issue / loose linkage ? I am hoping it's not the syncro or my first gear or anything that big.

Anyone have experience 1st gear pops out like this before and know of any fix/upgrade kit?

This is probably not relevant, but I had this problem with my 2.5 tdi A4. Only it kept jumping out of second gear, it started doing it on the odd occasion, but this just got steadily worse to the point that I used to skip second! Needless to say I had to have a new 2nd gear fitted. ?750ish as I remember :(