Cylinder with Internal Leak

Drawing / sketch required please.

Cylinder is just a vessel. Do you mean you have a piston somewhere?

where is the "internal leak?

Where is the pressure difference driving this "internal leak"? - You say equal pressure so why is there a leak?

Sorry, but this is very unclear to me based on words only.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

If you have equal pressure on both sides of a piston, you do not have a leak. The pressure in a cylinder typically leaks across the seals to the rod side, which requires a pressure difference to leak the cylinder contents to the rod side and in which case, pressures are not equal, or it could leak through the head gasket, in case of the cylinder being closed by the cylinder head above. "Internal" leaks within a cylinder are not really possible, as pressure is the same everywhere in the cylinder.

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."