It was mentioned to me by a Catalina sailor that often people do not peek at their o rings on the mentioned caps, therefor, allowing i.e. water to seep into the fuel tank, deck/rain water to seep into the fresh water tank, etc. So....I checked my 1983 O'Day caps and there were NO o ring gaskets. So....of course I bought some. When I went to put them on and screw the caps into place, I noticed that the cap nop does NOT mount flush, but instead sticks up. My conclusion is: a)my caps do not require o rings b)I really need to torque down when tightening, I mean really torque down in order to get them flush. All of you O'Day owners, do you have o rings? I think it seems wierd that NONE of my caps had them which makes me think they are not supposed to have them. However, the concept makes perfect sense. Please inform if you have info regarding this.