Had the exact same problem in my '02 S 6 speed and put in one of these from G-Box. This part plus fresh synthetic made a huge difference.
2ND GEAR POP-OUT UPGRADE-GBOX Transmission
I'd say it's 90% better. I still notice a little notchiness shifting into second when the 'box is stone cold in the morning, so I rev it a bit higher, skipping 2nd till she warms up (about 5 mins). There's never any grinding or popping out.
This is a lot less expensive to try first before a gearbox replacement.