Hi All, I am about to provide some TLC to Hakuna Matata as her deck varnish has 'cracked' in a few places (mostly where my weight is on the side deck!!) and the wood has immediately started to show some black specs and to fade around the area.  I am assuming that a strip back to wood in the local area, warmth to dry it out and then recoating with multiple layers of good Varnish would be the way to go - I don't want to embark on a full deck refurb as the problem is only in a couple of places.  Thoughts? 

I'm in the same situation with The Dream Machine. Frost has excentuated it. 

I have used light oxcalic acid to lighten dark patches.

Just about to say the same as Gareth.   You can buy oxalic acid on the web as it is sold for wood treatment or if you have a local beekeeper friend ask them as they use it to cleanse hives.
 
Small of amount of care needed as it is a weak acid and also slightly toxic - lethal dose in yhe order of 70grammes!  Wear rubber gloves and wash well with water after it has done its job before drying and varnishing.
 
Also removes rust stains from sails. 

Got some last week from these guys, very quick delivery - http://darrantchemicals.co.uk/index.php?route=product/search&search=oxalic%20acid
BTW its also great for getting those horrid brown oxide stains off fiberglass hulls