Anyone tried touprett white glazing putty?
Protect the cill but DO NOT cover it tightly with polythene or similar as this will cause condensation/sweating and you will degrade the timber even more.
You need air flow to dry the cill out so if you have to cover it make sure that air can ‘flow’ and let it dry naturally, sorry but it will be slow.
Cannot comment on the dec side of things. Hope this small input helps.