Yes it's just an o-ring in there, it goes hard as they all do and leaks. That's also just a random bit of hose bodged in - the proper hose is only 5-8 quid, just google breather hose kit as the other one just down and nearer the pulleys tends to leak when old as well.
Doesnt look too bad a buy - can't buy a D1 now that doesn't need a solid week (or solid year) of welding to bring it upto spec nowadays, I'd also stick a cambelt on as well before too long.
Bit odd it still has the doughnut flange rear prop, as it's been lifted. Also a shame about the numberplate
