Camellia problems

Guernsey Donkey2

We have four very mature large camillias in our front garden.  They have grown happily for over 100 years and each has a different coloured flower.  At the moment all of them have buds and one or two of them are now in flower which is normal.  However the smallest isn't well - part of the plant has died and some of the leaves are turning yellow - although some parts of the plant are healthy and producing buds.  Can anyone advise us please.

Guernsey Donkey2

I agree, it would be a shame to lose this plant, it has served us well for 40+ years, and others before us.  The main stem was split by a falling pine tree around 18 years ago, but seemed to rally round and produced amazing flowers every year.  I will look up liquid seaweed, thanks for the suggestion philippa