Zanussi GC 20 M Instructions For The Use And Care page 19

Maintenance
Check at regular intervals the condition
and serviceability of the gas connection
hose and pressure regulator, if any; in case
of malfunction, do not repair but replace
the whole faulty part.
To ensure a smooth and safe operation, it
is necessary to periodically grease the gas
taps.
Servicing should be carried out as follows:
remove the knobs and slide out the front
panel after removing the securing screws.
Unscrew the two screws to be found
next to the gas tap shaft.
Slide out the cone and clean it thoroughly;
finally, apply a thin layer of grease of a
type non-soluble to hydrocarbons and
suitable for gas taps.
Make sure that no excess grease obstructs
the gas tap holes.
Refit everything very carefully reversing
the above procedure.