Vented v Unvented Gas / Petrol Capa

[Pagodatastic]

Dear Pagoda Fans,
My gas / petrol cap leaks form time to time. After much research it seems it could be down to the fact my locking Mercedes cap is vented. I notice there are 2 on the market. A vented and an unvented.  Does anyone out there know how to identify which cap I have?
Visibly how do I identify whether my cap is the vented or unvented version?
Thank you so much
Best
S

[WRe]

Hi,
all our cars use non-vented caps because the fuel tank is vented through a seperate line.
Most of our cars have a vented fuel system except late cars with US emission systems. They use a non-vented system, see
- https://www.sl113.org/wiki/Fuel/Venting system and
- https://www.sl113.org/wiki/Fuel/VaporTank.
...WRe

[Pagodatastic]

Thank you for the reply.
Does not really solve my issue however.
My car is a US version 1969.
As I mentioned the cap leaks (changed the seal of course)
Before I spend $300 on a new unvented locking cap how can I tell my current cap is the venting version? 
(Millers Mercedes parts sell them both)
If I already have the unvented version I know the problem lies elsewhere. (Plus don't want to waste the money)
Thank you

[WRe]

Hi,
original non-vented caps are marked "ohne Lüftung".
...WRe

[Pagodatastic]

Brilliant,
The info I need.  Will go and have a look.
Danke
Best
S

[Pagodatastic]

BTW if it is a vented cap can the vent be sealed to turn it into a non vented cap?
That would save the Money of a new cap which would be welcome. Can spend that month elsewhere on the car.
Thank you

[Pagodatastic]

It says: OHNE ENTLUFTUNG
(See attachment)
Please can you confirm of this is vented or not
Thank you so much
Best

[calicoup]

OHNE ENTLUFTUNG Translates to “WITHOUT VENTILATION”

[Pagodatastic]

Thanks so much.
(Just did a google translate myself)
Appreciated
Best