Here is little bit of Poulan S25 tips from experience: Those are very good saws.
I've got two of them S25 Poulans and they are one of my favorite small saws. Almost throwed the first one in the trash, it was fished out of the trash, but the guys on here told me it's a diamond in the rough when I asked about such, so I fixed it and stumbled across another later. They were built back when Poulan made good stuff. (and I'm not a lateer model Poulan fan) Old fuel lines are usually their main problem and the fuel lines are not easily replaced, but you can find You tube videos of such to give you an idea of how to go about repairs. Some S25's have slightly different fuel line routes. Lots of owners manuals and parts lists available on-line to download free. Sears/Craftsman sold few of the S25's re-branded as Craftsman with Sears long model number and were different colors other than dark Green. Later model top handles by Poulan/Craftsman were not of the good quality of the S25's
The vent on that cap is a standard Homelite duckbill. (usually orange or red in color and some duckbills are pricy each at around $6 each for the genuine ones. The bulk ones of 10-20 at this price is China clones and iffy on long life around oil.
Before getting a replacement duckbill you need to very gently and carefully remove that star washer from the cap by gently going around the edge of the washer with something like a o-ring pick. If you break the little plastic hollow tab that the star washer is on you will be SOL, because the duckbill vent has to slip fit over it and the star washer holds the duckbill in place. The Poulan duckbill vents in the cap were black and become gummy and rotten over time and may be pieces of such under the star washer.
Those caps were used on the Poulan S25, S25DA, and S25CVA series. Very good saws built for the long haul, Back in the 70's I think maybe they were priced about same a the Homelite Super EZ's at around $150 back when a dollar was actually a dollar. Green in color, maybe some red. The later versions had electronic ignition.
They had 16 inch bars, light weight and will last forever with just little bit of TLC. I have two of them that I use quite often as trim saws after I get a big tree down.
I even got carrying cases with mine and I carry a extra fuel cap.
Every once in awhile a gas cap will surface on flea bay at a reasonable price. Some are called vintage and priced out of site at around $20 and the duckbill vent area bad/broken or no duckbill inside or the old black gummy one.
You say your vent was spraying gas when running. Normally the gas tank on those does not pressurize and spray. The carbs just sucks gas. If you ever run it completely out of gas it takes lots cranking and full choke usually to get gas to the carb due to the long fuel line, then 1/2 choke when it pops.
Maybe your tank was completely full and gas getting warm and spitting out??????
It's usually worth the effort to keep that little jewel running. You will like it when all is correct. Be careful when installing the top cover and get the choke tab and fuel lines located properly. Check yours and see that dust cannot sneak into the air box under the air filter. You will get the idea when you look for such. I had to cut and make some foam to block off some of the sneaky places for dust to get in around the air box. The old small pieces of foam filter in those places rot and goes away.
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