For years, LHM has leaked the oil from the tank to prevent Haydrauk from producing the solution for it.
With the parts included in this package you forget about the oil loss.
The main cause of the problem is the inward embedding of the upper part due to the pressure created by the hard wire attaching the lid to the tank.

The internal device in the package corrects this tendency by pressure to the outside and prevents the oil from leaking with the new generation seal.