Thank you for giving your experience re the condensation/ water damage , I have some of that to deal with & I have also been experimenting with teak stain , I have dabbled in minor furniture restoration & found that to get effective repairs you sometimes have to use tricks like colour matching with stain or oil paints , eg painting wood grain on severely damaged wood then re coating complete panels.
The hard part is getting the correct lustre on the topcoat to match the rest of the interior , hence my question regarding original application methods & materials . The previous owner has attempted some repairs but not well !, eg sanding marks out across the grain & then applying a clear matte varnish , resulting in light patches which will necessitate stripping the entire panel I believe .in the absence of the knowledge of the original method / material used I shall have to strip the back of a cupboard door first & then experiment with differing stains & varnish mixtures until I crack it , very time consuming & expensive but I see no other option although when it is done it will allow me to maintain the wood effectively. As far as external wood is concerned I just use wet & forget to keep it clear of mould & let it silver, I believe it’s best to not sand it in anyway & keep mechanical cleaning to a minimum to prolong the life of the deck ! On most teak decked boats I have seen , it’s the thinness of the teak or failure of the joints / fixings that cause their demise .
All insights & experience are of value & are very much appreciated.
Best wishes Les