What do you mean by top? Is your picture turned sideways? Where is the air coming from, there should be no leaks. If anything they will be coming from the connections of the air lines. I put ptfe tape round the threads to make the seal.
The top is at the same end as the airlines, the glass faces down. On my silent compressor the valve at the bottom of the glass has a weak spring and so I have to manually pull the valve closed. Once the pressure has built up it stays shut.
Lee