my power steering cap leaks. i wonder if i'm missing a gasket or o ring. can someone verify if theres any......

 

It will leak if the system is over filled, its supposed to do that to prevent over pressurization and blowing a seal or a hose.

 

Same kind of issue... both my ACE and power steering reservoir caps have a very subtle amount of fluid leaking. I was going to start looking for new seal or caps.
Good to know the cap allows a little pressurized fluid to release.
Piece of mind.

 

the fluid shouldnt be under any pressure. it just churns around in there as it gets pumped back into the reservoir

 

If overfilled it would have pressure, it needs the expansion space.

 

I had a minor leak, the reservoir always got a slight oil film on it. Took out the O-ring from the cap and inspected it. Looked OK, but the cross section was only 3mm horizontally, while 3.5mm vertically. Looked up the standard sizes and found an O-ring that exactly fits: AS-209 (AS568 SAE). Went to my local hardware store and found it for $0.69:



The cross section on the package is not accurate, it's measured 0.139", not 0.125", but which is exactly standard size. Now the cap sits really tight in the reservoir. The two O-rings compared (left = new, right = old) shows clearly the difference: