Turn Signal Indicator

Couple of questions......

I removed the cable and socket from the underside of the hood and unbolted the lamp fixture. The bulb is stuck in the fixture and I'm hesitant to apply any force. I put some penetrating oil around the threads in hopes this might free it. Is the bulb held in via the threads?

Also, any suggestions on materials to make a new gasket out of? I'm pretty sure no one sell just the gasket.

Thanks.