Signs of brake fluid overflow spill

[trygve]

I got back from Laguna Seca last Monday and noticed some brake fluid on the front trunk floor and wall (they're bare, this is a Spec Boxster) that had clearly dripped down from around the reservoir area. It looks to me as if it had overflowed the cap (which was tight) and dripped onto the reservoir top, which has a lip that will retain a tiny amount of overflow, but was too much for that. It was a small enough amount to be wiped up easily with a rag, but it was a bit of a mess all over the trunk wall and floor.

I can definitely see how this would be expected if the brake fluid reservoir cap is not well sealed. My cap does not have a gasket ring of any kind -- should it have one? It is just a plastic cap threaded onto a plastic tube, and that does not strike me as creating a good anti-spillage seal in the face of sloshing about under track conditions. I hope it's not coming from anywhere else (I don't see signs of such).