Tail Light Leak.. Help..

[BMWLOCO]

Noticing some water coming in to the jack area when it rains pretty heavy here in the gulf coast. I saw some water on the tail light. I pulled the tail light off and repositioned the seal/gasket and it was dirty and not fitted pretty well.

Can I just replace the gasket with a generic rubber gasket from home depot? or do I have to order the OEM one.

Also, the plastic trim piece that goes over the rear door is loose. This might also be the culprit.. or not!..

Thanks in advance.