A guided wave radar level gauge for determining a filling level of a product contained in a tank, which level gauge comprises: a transceiver for transmitting electromagnetic transmit signals and receiving electromagnetic echo signals reflected at a surface of said product, a probe, connected to said transceiver and configured to extend into said tank and to guide said transmit signals towards said surface and to guide said echo signals to said transceiver, a sealing arrangement comprising: - a hollow housing, - a conductor extending inside said housing for transmitting electromagnetic signals between said transceiver and said probe, - a dielectric sleeve arranged inside said housing and surrounding said conductor, - at least one gap (26, 27), formed between said dielectric sleeve and an adjacent, electrically conducting surface, said gap having an open end facing said tank, allowing the tank atmosphere to enter and condense in said gap, and - an electrically conducting coating (28, 28a, 29, 29a) provided on a surface of said dielectric sleeve facing said gap, and in electrical contact with said adjacent, electrically conducting surface, so that an impedance between said electrically conducting coating and said adjacent electrically conducting surface is sufficiently low at an operating frequency of said gauge to reduce an influence of any medium present in said gap, characterised in that said at least one gap includes a first gap formed between said sleeve and said conductor and in that said electrically conductive surface coating includes a first electrically conductive surface coating provided on an inner surface of said sleeve. a transceiver for transmitting electromagnetic transmit signals and receiving electromagnetic echo signals reflected at a surface of said product, a probe, connected to said transceiver and configured to extend into said tank and to guide said transmit signals towards said surface and to guide said echo signals to said transceiver, a sealing arrangement comprising: - a hollow housing, - a conductor extending inside said housing for transmitting electromagnetic signals between said transceiver and said probe, - a dielectric sleeve arranged inside said housing and surrounding said conductor, - at least one gap (26, 27), formed between said dielectric sleeve and an adjacent, electrically conducting surface, said gap having an open end facing said tank, allowing the tank atmosphere to enter and condense in said gap, and - an electrically conducting coating (28, 28a, 29, 29a) provided on a surface of said dielectric sleeve facing said gap, and in electrical contact with said adjacent, electrically conducting surface, so that an impedance between said electrically conducting coating and said adjacent electrically conducting surface is sufficiently low at an operating frequency of said gauge to reduce an influence of any medium present in said gap, characterised in that said at least one gap includes a first gap formed between said sleeve and said conductor and in that said electrically conductive surface coating includes a first electrically conductive surface coating provided on an inner surface of said sleeve. - a hollow housing, - a conductor extending inside said housing for transmitting electromagnetic signals between said transceiver and said probe, - a dielectric sleeve arranged inside said housing and surrounding said conductor, - at least one gap (26, 27), formed between said dielectric sleeve and an adjacent, electrically conducting surface, said gap having an open end facing said tank, allowing the tank atmosphere to enter and condense in said gap, and - an electrically conducting coating (28, 28a, 29, 29a) provided on a surface of said dielectric sleeve facing said gap, and in electrical contact with said adjacent, electrically conducting surface, so that an impedance between said electrically conducting coating and said adjacent electrically conducting surface is sufficiently low at an operating frequency of said gauge to reduce an influence of any medium present in said gap, characterised in that said at least one gap includes a first gap formed between said sleeve and said conductor and in that said electrically conductive surface coating includes a first electrically conductive surface coating provided on an inner surface of said sleeve.