Mine is an unvented rocker cover cap. Seals well. No problems here.

Mine is the locking type and is also vented.

Don't know why you can't see the pictures... I just sent you an email with the pics.

I thought those were for filling Al....either way, if it spills it still makes it's way to the paint...lol
notabmw....no pics showing

I didn't know there was once a vented cap for the classic.

I found that a new cap I had was leaking.  It was a cheap repro one and the "rubber" seal had ripped.

Now l know why most minis imported from the U K had those funky straps attached to the neck of the petrol cap- Obviously to help keep the petrol off the paint-

What are those straps called in the  U K-?  Some come with a Union Jack design printed on them

BIG AL-

Using a valvedcap from a '70's Chevy van works, it has vacume and pressure valves built into it for emissions...combined with the tips below....

While on lapping days, I've been flagged for doing just that. I mean who doesnt want a 91 octane wash?

Another shot.

The problem is the fuel spills out of the vented cap.  Mine was doing that so I made a baffle with a vent so when the fuel hits it it has 3 baffles to bypass before it reaches the cap original vent.  Result, no more fuel pissing out, and the cap can still breath.

No.

Make sure the tank neck isn't damaged. Many are twisted at the top or have the bayonet ramps inside damaged over the years by villains levering locking caps off to steal fuel. If so, a new seal won't fix it.
My RH tank neck was damaged bad, so I bought a new dummy neck. I cut it and the tank neck then gas welded them together (with tank washed out then filled to bottom of neck with water during welding). Joint is inside the grommet so can't be seen.

[edit] The gas caps should be sealed, not vented. The vent lines are in the top of the tanks.

It's fairly common. Sometimes it gets a little out of hand. See attached pic.

The seal on a forty-year-old-cap likely won't be in the best of condition. Start with a new cap. While you're at it, check to see that your vent line isn't kinked.

 

The real fun comes when you run twin tanks and you can spill on both sides. I'm very lucky to have a shop near the local hose and gasket shop ( Hampton Rubber Co. ) after putting up with spills and running only half full for 78000 miles on this one, I paid them a visit. They wanted to show off their new water jet cutter. I ran out to the car and removed the rubber cap gasket for lack of a better word and had them cut gaskets of their best fuel resistant material in several different thicknesses. I played with changing them out till I could fill tanks and slide around corners without spills. That batch was free perhaps I should figure out which worked and have some done and sell them. Having delt with spills since 1968 and the solution was so simple.

Steve (CTR)

Do all Mini's suffer from leaking gas caps and therefore lead to fUgly stains down the back side?  I have been looking for more answers on this and not seeing a lot out there, but maybe it is one of those things that just are what they are.

If so, are there any ways to prevent this - or does the Mini tank not have proper ventilation?

TIA.