Good to know you had success. I had some difficulties coping with water strains (condensation) on veneered wood. I tried oxalic acide with no success. Sanding hardly restore the original colour and each sheed of wood are so thin … I’ll follow your track.
2- restoring discoloration
I’ll give a try to Net-Trol Wood Cleaner & Colour Restorer
3- varnishing inside
After some sanding veneered wood inside (400 emery wet paper is more than enough) but leaving some old varnish (eg, not to bare wood) I apply International schooner or schooner gold with 30 to 50% international matting additive. Still, under some light conditions (sun lignting parallel to the surface) the result appears very slightly dull. I have been advised to try some light “steel whool”. Alternatively I’ll try some 1000 or 3000 emery wet paper. I’ll let you know.
Varnishing massive wood is no problem : very light layers and some light sanding (400, wet)
4- difference in colour on picture 20161004_135719.jpg
I refer to the change in colour on the solid (eg not veneered) wood at up and left angle of left window. I faced that change in coloration when revarnishing wooden frame of dinette table in the helm house. I feel the difference is due to a difference in absorption of varnish by the wood, I think old varnish remains prevent absorbtion and yeld lignter colour. I’ll have to redo the varnish after deep sanding to homogenise the absorbtion which is no problem with solid/massive wood.
Wood framing(massive) of the staircase to the galley has the same symptom. I’ll do some deep sanding and wait for monthes before varnishing, to dry out. I’ll keep you informed.
I also suffer from dark dots or stains here and there, especially on outside veneers covered with Cetol. Probably some fungus déveloped where water penetrated. Found no solution, oxalic acide not being satisfactory. Was advised by old sailors to extensively sand to remove dark parts, which is not a solution with veneered wood.
Most of the condensation under the windows and rubber frames stopped appearing since I keep here permanently under tarpaulin in winter. No more condensation.