348 spider master cylinder cap leaks

I found a nice puddle of brake fluid under my car about a month ago. The cap had leaked into the trunk and eventually got on the floor. I thought originally, maybe the cap wasn’t tight enough. I cleaned up and put the cap on tight. I drove the car 3 or 4 times over a month and the last time it leaked again. It’s definitely the cap. The cap gasket looks to be ok. There’s a small slit on the top of the raised portion of the gasket. The cap has a channel to allow fluid to leak out.
I don’t have any other brake fluid leaks that I can see
The cap and gasket doesn’t appear to be available.
Not sure if there’s an issue with the brake system. I have not seen the fluid level change since first big leak

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The fluid level is below max line. After each drive I have checked fluid level and it’s about the same. Level is at seam of the reservoir
I think something is causing the fluid to rise??!

 

I have added no fluid prior to leak or since

The fluid was above the max line just a hair. I pulled out some fluid (anbout 1/3 cup) and got it at just below the max line. I drove the car and checked level when I got back. The level dropped about 3/16 but is well above the min.
I assume the level will go up and down. I will drive and check a few more times this weekend.

 

I just had engine out done. I know fluid was changed 2 years ago. I’m assuming it was changed again during engine out last December last year. I will drive and check level after and see how much level changes
My brake pedal is firm and has short travel. It feels good