Cap is on tight, not sure why it's leaking. Any ideas?

I know it's connected to the ac compressor. I had the compressor replaced last summer and the PS reservoir seems like it's at the slightest angle. Could that cause it?

Any other thoughts?

Do the seals around the cap wear out? Replace cap and all will be fine? Or does this mean I may have a leak in the system letting air in?

Thanks.

 

Going to try changing the cap first and if that doesn't work, I'll change the reservoir. It's only $25 for an OE part. I haven't had to add any fluid as it still looks full, so it must not have leaked that much. I just put 3400 miles on the truck in the last two weeks driving it to Florida and back. Other than this cap leaking, it did great and got 21 mpg constistantly going 75 mph on I-95.

Had a friend inspect it at his shop yesterday and he said the rest of the system looks fine.

 

What did this end up being?
I have the same leak around my cap