'99 DR350SE - Carb leaking gas into intake

I've read lots of threads about this problem and decided to replace the o-ring on the needle valve. I recently rejetted the carb and noticed the needle seat o-ring was in bad condition. After rejetting, the bike ran perfect for about 2 weeks and then gas starting leaking.

The o-ring is discontinued by Suzuki, so I went to Home Depot and matched it up best I could.

The old o-ring had shrunk to a point where it wasn't sealing anymore. I had gas leaking into my intake manifold and draining out of the bike when parked.

When I installed the new needle seat o-ring, I had to press the seat back into the carb with lots of force. After reassembly, the gas leaking problem was worse.

Question #1: Does the needle seat need to be move up and down? Or should it stay in place?

I figure the o-ring I used is either too big or the needle valve is not sealing and needs to be replaced.

Question #2: What is the root cause for gas leaking into the intake manifold? Leakage at the needle valve or seat?

Any help you can provide will be appreciated. Thanks

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