Personaly I would prize the bottle from the master cylinder.(the last thng you need is solvents/cleaners entering the MC as it is likeley to FUBAR the seals )
You may or may not need to replace the bottle seals after doing this, it would depend how prerished or brittle the seals have become.
I would then either soak the bottle in some Jizer or the likes or place the bottle in some very warm/hot water. Add some washing up detergent & a generous helping of domestic bleach. Then soak overnight.
Hot soapy water & bleach will often work wonders of clear plastics
It may be the case that UV, heat & sheer age has got to the plastic & no amount of cleaning will bring it back to life.