I'll use limescale remover or Cillit Bang to soften the limescale then scrape it off. The silicone sealant I'll cut out, clean up the surface with sealant remover, and then after re grouting will reseal with Unibond anti mould silicone sealant.
For the grouting I plan on giving it a good soaking with thick clear bleach, use the Bosch Multi with "tile cutting" disc to cut back the good grout a little, or remove any loose grout. Maybe then another soak with bleach to kill any remaining mould spores. Then I'll regrout the whole lot with a white water proof tile grout. Normally I use Unibond powder tile grout.
It it then worth sealing the grout with Lithofin (the data sheet says it's for porous surfaces, waterproof tile grout isn't porous)?
Anyone recommend a different approach, or different products?