Cork?
Could you create a step by step directory using photos, patience, a gamble and all the marvellous enthusiasts on this site. I suggest starting by...
Silicone sealant :nightmare. Indeed not enough info. on project.What falls out can explain a lot. Fair condition:usualy one finds woodlice,ranging...
Your problem seems to be,that the wood won't get the chance to swell.I suggest clearing out all caulking,then once really clean;applying a flat...
Underwater. Appart from sussing any unwanted movement;loose or cracked stuff;caulking with cotton soaked in putty&paint.Plywood strip fillets?...