Spinflo cara hob?

SPINFLO CARA
5 Hob taps four the rings one the grill
One ring and the grill works each depresses to clear safety 'Lock off' the other three rings taps won't depress so can't be turned on.
On removing the knobs each of the 3 tap shafts had a furry white deposit around the tap shaft.
Would this (a) indicate a leak (b) what can I do to release the tap shafts so they plunge down clear of 'Lock off? Yes I am aware its a gas safe engineers job to remove and replace the hob.
Many thanks