Breather or non breather oil filler cap?

[Donzi GT250]

1990 OMC Cobra 5.7 each valve cover has bayonet style 1/4 twist style oil filler caps.
I have noticed oil residue on valve covers in the area of the oil filler caps.
I checked the original oil filler caps and they seem to not fit as tight as what I think they should.
The gaskets on the caps look OK but they don't seem to fit snug and seal when closed.
Can these caps wear out?
I went to NAPA and picked up a GM bayonet oil filler cap and this cap does fit more snugly and seems to seal.
But my question is should my OEM caps fit as loose as they do and when I replace the caps should I go with breather or the standard non breather style caps?
Thanks

 

[Kainon]

Re: Breather or non breather oil filler cap?

Breather oil caps arent needed in marine, like in auto, as with performance auto valve covers dont always have PCV Valve ports so Breather caps must be used so the engine doesnt build up pressure.

In Marine, non breathers are used and they should fit snugly and shouldnt leak, there is no baffle inside where the cap is to keep oil off the underside.

the tubes that goto the air cleaner do not use a PVC Valve as auto's do and they are open and have baffles inside to help keep splashed oil from entering the port, but oil laden fumes do make their way out with age which is why cleaning the Flame Arrestor is needed.